Begin or restore a game. You should get a message stating that debugging keys are now available. To use the cheat codes, press the keys listed below simultaneously. Changes the screen border color. Displays the number of statics, doors, and actors in the level.
Statics are things like food, ammo, pools of blood, etc., and actors are the bad guys.
Doors should be self-explanatory. Moves you ahead one level. To convert the X and Y values to coordinates that can be used in MapEdit, divide them by 65,536 and round down. A is in degrees ranging counterclockwise from right. Basically it just means that you're invincible.