Bring down the console with the Tilde (~) key and enter the cheats.
NOTE: Listed cheats will cause the game to display your name as "CHEATER".

GetSkill [Skillname]
Lists available skills, add a Skill Name after cheat and it tells you the
skill number. 

CheatSkill [Skillname] [Amount]
Use to set your skill number to whatever. Example = "Cheatskill skshooting 99".