be nice kids, we've all been there
I don't know what Dark invader is, but i'm guessing your developing a basic space invaders game?
For learning purposes i suppose you could do the following:
1.) Make about 10 boxes as aliens
2.) make two boxes as spaceships
these are called placeholders, and you'll put your final models in later
Next step, Position them on the screen depending on where you want them, i'd say have Player1's box on the left side, and player two on the right.
Create a bullet array, perhaps 100 little plains/boxes again
Next, program a fire button to shoot out a bullet
Make sure to kill off the bullet after it goes out of scope (the screen / hits an invader)
and wolla you've basically made a space invaders game with 2 player.
You'll have to do the leg work though in finding out how to code each part.