How do I send an item to a person i sold it to on ebay?

ok so i didn't know how to put the question right i think. so i've never sold anything on ebay and im so confused what do is use fedex or ups can i use just the post office?? idk and i dont know how much it costs to send it so i dont know how much to charge for the shipping or how long it'll take. can i just take it to a ups or fedex store and theyll do the rest? im really confused