Paypal is a method of paying for your product - when you've brought something before, I assume you sent a cheque or postal order then? Paypal is the most popular as it's secure and doesn't require typing in card details, plus it's instant payment for the seller. I think they charge a nominal fee though for every transaction, but it's worth opening an account with them - as a seller or a buyer. I've used it to buy and sell things, and never had a problem with them. Think the address is www.paypal.com
Everybody starts with no feedback so don't worry too much about it. You could mention it in your advert that you're a first time seller if it worries you, but people won't mind as long as they want the item enough. Just make sure you do a good job, describe it as it is (including any stains, tears etc.), and post it to them promptly and you'll have your first good feedback as a seller.