Easy to set up/get started. Go to the top of "my Ebay" and hit the "sell" tab. It's pretty straight forward from there.
With regards to postage, it's a bit of a guessing game, although you could get a scales and weigh everything properly and then work out the postage.
Bear in mind Paypal fees. If you can, try and get the buyer to collect and pay cash on collection. You'll still have to pay Ebay fees, but won't have to give Paypal their cut. It's worth doing. One mans trash is another man's treasure - or something like that! :-)