You basically go in, and let them know who you are if you are already registered. If not, you can register at the polls with any proof of address. Then you are given a ballot (D or R if you are registered such), or asked which primary you would like to vote in if you are an Ind. You are handed a ballot, go into a booth, mark it in for Ron Paul, come out and hand it to the person collecting ballots in towns or put it in the counting machines in cities, then if you were registered Ind going in, you can switch back to Ind on your way out the door.
You then go home and pace for hours until the results come out.