Adopted from:
http://en.wikipedia.org/wiki/Salsa_music
http://en.wikipedia.org/wiki/Salsa_dance
http://www.salsanewyork.com/ourdancemusic.htm

[different steps]

On One and On Two

Salsa danced according to the above description is called Salsa on One, or briefly, "On One", because it starts on the first count of the 8-beat rhythm. If the first step (with the left foot) occurs on count 2 or 6, it is called "On Two". This Basic Step pattern and timing are known also as "Power 2", "Palladium 2" or "Ballroom Mambo" style. This creates a distinction from another step pattern known as "NY Style 2" or "Eddie Torres Style".

Some consider dancing "On Two" to work more closely to the clave rhythm, the most basic rhythm of salsa music, as the steps start on the first tick of a 2-3 son clave. However, dancing "On One" hits just as many beats in the clave and hits the first tick if the music is using a 3-2 style son clave. In short it's a matter of personal preference which counting to use, and most people prefer the counting of the style they were taught first when they began dancing salsa.

Q:"Should I wait and become more profficient at on1 before starting on2?"

A:"On2 is actually a different dance to Salsa, on2 is Mambo and its in the minority so i would recommend sticking with Salsa."

http://www.uksalsa.com/Chat/on2/t471.html

[different styles]

Salsa styles
There are many characteristics that may identify a style. There may be different step patterns, different timing of steps, particular movement on the dance floor (eg:slot, circular), dancer preference of turns and moves, attitude and others. The presence of one or more of particular elements does not necessarily define a particular style. For example, many styles can be danced "On One" or one style may be danced "On One" or "On Two". The following are brief descriptions of major "recognizable" styles.

Colombian style
This style is common in Latin-American countries. The leader and follower do most of the movements while standing in place. It stems from the Cuban style. As such in many patterns the leader and follower turn around each other, although not as much as in the Cuban style; in fact, in several parts of Colombia, salsa is danced with very limited or no turns at all.

Los Angeles style [LA]
Los Angeles style
Developed in recent years (some say between 1999 and 2002), this is a style of salsa much influenced by Hollywood and by the swing & mambo dances, thus being the most flashy style, which is considered "more show than dance" by many. The two essential elements of this dance are the forward/backward basic as described above, and the cross-body lead. In this pattern, the leader steps forward on 1, steps to the right on 2-3 while turning 90 degrees counter-clockwise (facing to the left). The follower then steps forward on 5-6, and turns on 7-8, while the leader makes another 90 degrees counter-clockwise. After these 8 counts, the leader and follower have exchanged their positions. The Vazquez brothers are widely credited with developing the LA style of salsa. Tony Cordero and Robert Menache helped spread the influence of the LA style to Long Beach and Orange County. Luis taught in LA until 2005 when he and his dance partner Melissa Fernandez moved to Lugano, Switzerland. Here is a link to his bio: http://www.massalsabrava.com/bio.php His Brother Johnny moved to Valencia, Spain in 2002, together with his dance group Imperio Azteca. http://www.johnnyvazquez.com Both brothers decided to move to Europe because of business aspects. Nowadays, the market to sell their style of salsa in Europe is much bigger than in America. Almost every other weekend of the year there is a Salsa Congress somewhere in Europe.

New York style or Eddie Torres style [NY]
New York style or Eddie Torres style
The "NY Style" is a combination of the "On 1" and "On 2" systems. The timing of the steps are on the 1-2-3,5-6-7 as in "On 1" but the breaks (where the body changes direction) occur on the 2 and 6 as in "On 2". NY instructor Eddie Torres developed this step pattern around the late 70's and the 80's and its definition is quite clear since he is still alive and his followers are keen to keep the style intact. This is their description of the step: Description of "On Two" on salsanewyork.com There are many "socials" in NYC or nightclubs that dedicate on playing only mambo or salsa.

[different Rhythm and music]

Rhythm
 
A pair of claves, commonly used to play the clave rhythm.Salsa music is traditionally based on a 4/4 time signature, and is mostly phrased in groups of two bars (eight beats), such as recurring rhythmic patterns and main phrases of the chorus. Typically, the overall rhythmic patterns played on the percussion instruments are rather complicated, with several different patterns played simultaneously. The clave rhythm is an important foundation of salsa; all salsa music and dance is governed by the clave rhythm. The most common clave rhythm in salsa is the so called son clave, which is eight beats long and can be played either in 2-3 or 3-2 style. The 2-3 version contains two clave strikes in the first half of the eight beats and three in the second, while the 3-2 has the halves reversed.[24]

Instrumentalists do not generally play out the exact clave rhythm, except when using the percussion instrument also known as claves. In most other cases, the clave rhythm simply functions as a basis for the instrumentalists and singers to use as a common rhythmic ground for their own musical phrases. The instrumentalists emphasize the differences of the two halves of the eight beat clave rhythm; for example, in an eight beat long phrase used in a 2-3 clave context, the first half of the phrase is given more straight notes that are played directly on beat, while the second half instead contains notes with longer durations and with a more off-beat feeling. This emphasizes that the first four beats of the 2-3 son clave contain two "short" strikes that are directly on beat, while the last four beats contain three "long" clave strikes with the second strike placed off-beat between beats two and three. Salsa songs commonly start with one clave and then switch to the reverse partway through the song, without restarting the clave rhythm; instead, the rhythm is shifted four beats using breaks and stop-time.

Clave

A pair of claves, commonly used to play the clave rhythm.

The Clave - What is "Dancing On Clave"? -  The clave is traditionally a wooden instrument consisting of 2 sticks which are struck together to make a clicking or tapping sound.  Nowadays, sometimes it is a plastic hollow rectangular "box" which may be hand-held or mounted on the drum set - the timbales, cowbell, cymbal, woodblock, etc.   And sometimes the clave rhythm sounds come from other sources, such as the drummer tapping the side of a drum, the conga or bongo player's beat, a clave rhythm from the singer, piano or other instrument, etc.  In Spanish, the word "clave" means a "key", like a "key word" or the "key to a code".  In salsa music, the clave rhythm establishes the key or structure of the song.  Directly or indirectly, all the other instruments and the singers in the band are guided and structured by the clave rhythms.  While it cannot always be heard in some salsa music, the clave's beat always underlies the rhythmic structure of good salsa.  While there are various clave rhythm patterns, the "Son Clave" is the one used in the classic, mainstream New York Caribbean-style salsa music preferred by New Yorkers for On 2 dancing.  This clave is played within 2 measures of 4 beats each, a total of 8 beats.  But it is only tapped on certain of those 8 beats in the 2 measures.   There are two son clave rhythm patterns:   the 3/2 clave and the 2/3 clave.  The 3/2 clave is struck on the following beats:  1, 2 1/2,  4, 6, 7.  The 2/3 clave is struck on the following beats:  2, 3,  5, 6 1/2, 8.    The clave creates a complex, syncopated, unevenness in the rhythmic structure that builds a tension in the group of 3 taps, and then releases or resolves that tension in the group of 2 taps, once in each of the 2 measures.  It does this by going against, and then rejoining, the regular 8 beats, a little like one instrument playing in 4/4 time, and another playing in 3/4 time simultaneously.  This syncopation fascinates and inspires those more experienced On 2 dancers who are particularly in tune to the music, and affects the way they feel and move when they have reached the level of the dance where they are truly "dancing in the music".  

You may have heard the expression "Dancing on Clave" to describe New York On 2 mambo.  This needs some clarification.  Actually, this is a loose expression to mean that the clave contributes to the 8 beat rhythmic structure of salsa, and also affects how we feel and move to the music.  But we do not literally step to ALL the beats that the clave instrument taps out.  For example, the 2/3 clave instrument taps out 2, 3, 5, 6 1/2, 8, while we step on 1, 2, 3, 5, 6, 7.  So we are only stepping on the 2, 3 and 5 taps of the 2/3 clave.  And the 3/2 clave taps out 1, 2 1/2, 4, 6, 7, while we step on 1, 2, 3,  5, 6, 7.  So we only step on the 1, 6, and 7 of the 3/2 clave.  As an example of how the clave makes us feel and move, we break on 2 and 6, but the 6 break feels much more emphatic and part of the body than does the 2 break when we are dancing to a song with a 3/2 clave, because the 6 break is "On Clave", at least when it's audible in the music.  In contrast, when the song we are dancing to has a clear 2/3 clave structure, the 2 break feels stronger than the 6 break.  Many intermediate and advanced On 2 dancers feel this difference, particularly those who are closely attuned to the music. 

[my comments]

Very interesting and proves some of my feelings of the music, but still a little confusing. For the clave, with 1, 2 1/2,  4, 6, 7, you may clout with ur fingers to understand. Using slow speed setting to play the music and u should see the clave clearly. Anyway, somebody would like to share some sample video about above differences to me? People discuss On2, On1 and 2/3. But for me, a simple turn, music dominated and stable, is not easy to achieve...

http://spaces.msn.com/eparg/blog/cns!59BFC22C0E7E1A76!1027.entry