Different stunts can be preformed using the Stunt key. 

Normal Dive: Stunt key*Edit

High Dive: Jump, then press the Stunt key*

Slide: Crouch key followed by Stunt key while moving 

Wall-Flip/Backflip: While in mid-air and touching a solid object (wall, vehicle, player), aim the camera at the object and press the Stunt key.