Buying
Buying is easy and free, you may pay by bank deposit, paypal/credit card, cheque in the mail, and cash on delivery if you are allowed to pick it up your self. PayPal or using you Credit Cards is important for overseas buying because banks charge $20 each transfer overseas.
You can browse through categories to see the variety of items for sale, or search for items by typing a few key words into the search box. 
When you find an item you like, simply place a bid or choose Buy it Now
When you place a bid, the amount you put in the box is only you maximum amount, at the end of the auction you will only pay .5 cents more then what any one else enters up to you maximum bid, and then if they go over you maximum price then it is theirs.
Happy Bidding!

Automatic Bidding
Ever waited until 3 in the morning to bid on an eBay item or got up early to bit, so that you can bid closer to the end of the auction so people dont have days to consider spending more and more and going over your bid? an Auction sniper may be the answer for you. Contrary to the people that may think this is wrong, I believe you are just making a bid you would of normally make as if you were there 30seconds before the auction ended anyway, and if some one is will to pay more then it will still be theirs.
Many Auction snipers with free initial snipes maybe found doing a search for "Auction sniper".

Selling
eBay is a popular way to get rid of unwanted bric-a-brac and is also to grate for selling items as a businesses.
You may do a search for the item that you are going to sell, and see what category other people have chosen to put it in and what kind of description the have used.
Often you can do a search for you item and say find the home page for it and use the manufactures description of the item, this save allot of time, and you description will be professional and attractive to buyers, just cut and pasted.
Again you may search at eBay for similar items now on sale and see how they are described and what kinds of prices people are paying for them.