It's usually a round tip and you just make circles that stack on each other. I would try practicing on a piece of waxed paper until you get the hang of it, then do the cupcakes.
If you go into a craft store like Michael's or AC Moore, they will have a large round icing tip that you can use. You could always put the icing in a zip top bag and cut off the corner, it won't be quite as pretty and perfect, but will produce a similar result.
Welcome to DC. You are going to have a lot of fun here. And if you don't believe me to read "Stray Thoughts." I haven't stopped laughing for the past hour.