1. PayPal is your friend. Can't go wrong with it. You can set up an account, and send money to it from your own bank account, pay with credit cards and the buyer doesn't get your card or personal info, get paid with it, and deposit money into your bank account from it.
2. You have a few places that you can ship. US Postal Service, UPS, FedEx, DHL. Usually UPS is cheaper on bigger stuff, and regular mail is cheaper for little stuff. You have the option to buy insurance for items over $100, which is a good idea, since it's only a few bucks per hundred dollars of the item's value.
3. Sell/buy via paypal. Payment is accepted by the buyer/seller. The buyer's address is on the email repeipt that you will receive from paypal. Package the item. If you're taking it to the mailman, you have to physically write the return and recepient's addresses on the box. Just like you're sending a letter. If you go to UPS, FedEx, or DHL, you just take it to them, and tell them the address. They print up a shipping label, and put it on the box. You also have the choice of printing your own labels from home, and paying for shipping online. Then, just take it to the shipper, and drop it off. UPS, FedEx, and DHL will email you the tracking number, and give it to you on the receipt. The postal service, you have to ask for a tracking number, and it's a couple bucks more.