Press ~ to bring up the command console and put the cheats in there.

Code	Effect
Com_showFPS 3	Draw FPS
DebugUnlockPerkByAbility -1	Unlock Perks
DebugUnlockPerkByRequirement -1	Unlock Perks 2
cvarAdd g_inhibitAi 1	Dumb AI
cvarAdd g_permaGodMode 1 ( or type in god)	God Mode
cvarAdd g_permaInfiniteAmmo 1	Infinite Ammo
g_fov X - where X is the FOV number	Change FOV
dev 1	Developer Mode