Type the codes in-game just like in Doom:

nbreflect - mirror mode (cannot be toggled off)
nbponcho - toggles lava suit for 300 seconds
nbkfa - give full health, ammo, keys, and weapons
nbkeys - gives all keys
nbdeity - toggles god mode (can still take damage over 100 health)
nbff - doubles fire speed (this will stack!)
nbregularfingers - sets fire speed back to normal
nbhot - toggles superhot mode for 300 seconds
nbspoder - toggles climbing powerup for 300 seconds
nbshooters - gives all weapons
nbdeathless - gives full health and armor
nbfrog - increases jump height by .1 each time it's typed
nbman - resets jump height to normal
nbwoohoo - toggles a janky slow motion mode (careful, this can break the game when you switch levels!)
nbgotta - toggles double movement speed (also affects some vertical motions such as jump pads)
nbufo - toggles ability to jet up into the air by holding space bar
nbullets - infinite ammo