look at the platform game tutorial.
to make a background just make an actor called BG or somthing like that and put it in your game, and change its z-depth so it will stay in the back.
I suggest you start off with somthing simple,
AI can be anywhere from a simple go left and right and hurt you if it hits you're left and right or the enemy dies if you hit its head,
or it could be a bit more complicated with arrows and aiming stuff ect.
my knight archer game is an example of a bit more complex AI.
(see the .exe here:
http://game-editor.com/forum/viewtopic. ... 6175#16175 )