There are three kinds of fighting moves in San Andreas: boxing, capture and China Kung Fu, which are held in gymnasiums in three cities, as shown in the figure below:

When you walk into the gym where there is a red circle, there will be a conversation. Hold down the "Y" and confront the coach in the gym. After defeating him, you can get a special attack.

Usage of special attack: Go to NPC, lock with the right mouse button and press "F" to attack.