Enable the console from the game's in-game options. Hit the tilde key [~] to drop the
console. Type

seta thereisacow "1337"

and then press [Enter]. Now type

spdevmap

and then press [Enter]. An error msg will appear, ignore it. Klick END and resume a game
or start a new game.

Now in the game you open the console with the [^] - key again and you can type in the
cheat  codes here.

give all           Access all weapons
cg_LaserForceOn 1  Add laser sights to all weapons
jump_height #      Adjust gravity default = 39
timescale #        Adjust time default = 1.00
r_fullbright       Easier to see things
notarget           Enemies ignore you
give ammo          Full ammo
god                God mode
demigod            God mode but screen still shakes
noclip             No clipping mode
cg_drawGun         Removes your gun
cg_fov             Zoom with any gun