In its natural state, air-strafing requires a player to jump, release the "forward" (W) key, and simultaneously move their mouse in the same direction as their strafe key (A or D).
Understanding the CS 1.6 Strafe Helper: Mechanics, Legality, and Best Practices cs 1.6 strafe helper
Strafe helpers function by synchronizing your mouse movement with your keyboard inputs to maximize speed gain. In its natural state, air-strafing requires a player