Type them in the " ` " (or "Ö" for Swedish users) console:
Code - Result:
iwillsurvive - God mode
hitmewithyourbestshot - Computer Rocks!
closetoyou - Enemies do not see you
raindropskeepfallinonmyhead - Allow call for arty < 5 Shots > can be re-entered for more
takeittothelimit - Unlimited ammo
gamma # - Set gamma to #
turbo - Run faster