Start the game with the "+set console 1" command line parameter. Then while playing a game, press ~ to display the console and enter one of the following codes to activate the corresponding cheat function:

RESULT	CHEAT CODE
God mode	god
Invisible to enemies	notarget
.44 pistol	givemoretutorial
Sniper rifle	givesnipertutorial
All weapons	weapontest
No clipping mode	noclip
Slow-motion mode	timescale .4
Spawn indicated object	spawn [item name]