Edit the file "autoexec.cfg" in the "cfg" folder of the game and add "wirbelwind"(without quotes) to the end.
This will allow the key "`" to open the console.
Then enter the codes below, 1 to turn on the code and 0 to turn it off.
game_noai 1 - Disable artificial intelligence
i_am_an_alien 1 - Everybody including enemies becomes transparent,
happens only after loading a saved game
getitem x - Get item number x
setxplevel x - Set all squad members to x level
cheat_showall 1 - Show all enemies including NPCs
godmode 1 - Squad invulnerable