Press Ctrl + Alt + F3 to bring the console menu and enter the following cheats to get the corresponding effect:

Code - Effect

CheatWeapons 1 - All weapons
CheatImmortality 0 - Disable God Mode
CheatAmmo 1 - Full Ammo
CheatHealth 1 - Full Health
CheatNextLevel 1 - Go to Next Level
CheatImmortality 1 - God Mode