Press the tilde (~) key and type sv_cheats 1... Then you can use the following cheat codes:
god - Immortality
boost 101 - All weapons and ammo
kill - Suicide
thirdperson - Third person view
firstperson - First-person view
cl_forwardspeed, cl_backspeed, cl_sidespeed (number) - Increase or decrease player speed
give weapon_ (player's nickname) - Gives a weapon to the selected player
skin- (skin name) - Changes the player's skin
sv_clienttrace 999999999 - Extreme auto sight
mp_footsteps (0-1) - Switch to step. 0 disable, 1 enable
sv_gravity (number) - Changes gravity. Try to enter a negative value
