You can drop bombs with E and use a secondary item (when you obtain one) with the spacebar. Move around with the WASD keys and fire tears (Isaac's weapon of choice) in any direction with the arrow keys.
He has a few weapons and power-ups to help him through it all, though.
As it turns out, the basement isn't a very friendly place, and Isaac now has to deal with all sorts of nauseating abominations.
