Open the console by pressing ~ (tilde) during the game. Type any of the following cheat codes. 
 

Code:                                           Result:
tgm                                               God Mode
tcl                                                 No Clipping Mode
tmm 1                                           All Mapmarkers
advlevel                                        Advance to Next Level
getXPfornextlevel                           Advance to Next Level
showracemenu                               Modify Appearance
kill                                                 Kill Selected NPC
tfow                                               Toggle Fog of War
movetoqt                                        Teleport to Quest Target
resurrect                                          Resurrect Targeted NPC
coc testqaitems                               Warp to Room with All Items
coc megatoncommonhouse              Warp Back
unlock                                             Unlock Selected Item (Doors, etc)
Player.SetWeaponHealthPerc 100      Restore Weapon to 100%

Add Items/Spells
Use the code player.additem [itemnr] [nr]. This adds amount [nr] of item [itemnr] to inventory. Useplayer.addspell [itemnr] to add spells or aid. 

SEE CURRENT ITEM LIST: Link 

Example: player.additem 0000000f 5 to add 5 bottle caps. 

Set Skills/Attributes
Use the codes player.setav [skill], [nr] for skills and player.setav [attribute] [nr] for attributes. 

Note: Skills and attributes are written in small letters, together as one word. "Melee Weapons" turns to "meleeweapons". 

You can also use modpca [attribute] [nr] to raise attribute points. Example: modpca strength 5 will raise your Strength by 5. Max is 10.