As I remember because I haven't played for years:
You need at least 4 players to play to be any fun. 1 Dungeon Master and 3 Players. If you don't have that than go to a game store and look up events and find a group of people to join.
You need to a players handbook. Figure out which version you need or want to play with.
And you need a set of dice, they makes sets for D&D - - very common place. Then you're set.
And you have a girlfriend that wants to play D&D with you?!? Brutal.
Is fancy bread in the heart or in the head