tech help? (website, shopping cart, paypal)

I want to sell greeting cards from a web site. I'd like to buy a site template from templatemonster.com, connect it to a shopping cart of some sort, and give customers the ability to use PayPal. I have no idea how to do this, but I have a lot of beer. Can someone help me out? My guess is that it's pretty simple stuff, but I don't know the order of operations at all, and I keep psyching myself out. I'm afraid to get stuck doing something the wrong, cumbersome, or expensive way on account of some easily-avoidable mistake. Somebody please help me over this big, dumb hurdle. Seriously, lots of beer.