I finally got my power supply (an AC adapter with a micro USB port that also doubles as an Android charger) from the mail. I put in the micro SD card with the RetroPie image written on to it, plugged the power into the Raspberry Pi that I ordered two weeks ago, and it works!

I’ll have to try to plug in my PS3 controller and my new wireless keyboard that I purchased from Target up to the Raspberry Pi, get a few game ROMs (I have some SNES games I have in mind to put in), and I’ll be set!