OVERVIEW
There is no magic in Sword Art Online. No fireball slinging mages or illusion casting bards. Because of that, Sword Arts, or techniques, are the main abilities players use to gain an edge in combat. These techniques vary greatly and there are said to be so many the entire population could have different sets.
Because Sword Arts are basically just combinations of movements preformed at inhuman speeds, with inhuman strength, or with special effects, their damage is highly dependent on a character's weapons, not their level. This also means a character's Sword Arts will rarely become useless, even as they progress further into the game.
USING SWORD ARTS
In order to activate a Sword Art, a player must take up a specific stance from which the technique will initiate. Once the activation has begun, the user's weapon will begin to glow or gain another obvious activation particle effect. It only takes a brief moment after activation for the technique to be ready to unleash.
Once a Sword Art is used, the system takes over for the player and attempts to preform the combination of moves. If at any time during the technique you are blocked or prevented from continuing the combo, the system will drop control and the Sword Art will end. A player may also forcibly end a Sword Art at any time if they so desire.
RANKS
Sword Arts are ranked on a scale from E to S. E rank techniques can often be used as many times as a character wants, though they rarely have insane effects. On the opposite end of the spectrum, S rank Sword Arts usually have ridiculous effects with long charge times and few uses.
There are no limits to the strength or number of Sword Arts a character can learn. In fact, a level 1 character could have a dozen S rank techniques, though they still wouldn't be terribly damaging to a level 20 ogre.
CREATING SWORD ARTS
Developing new Sword Arts is something almost every player in SAO will do. All it involves is spending experience depending on how powerful the technique is. It's also possible to for players to teach other their own Sword Arts at a reduced experience cost.