I've used eBay on and off over the years. Here's a couple things I learned:
Some people put items out there at a ridiculously low price but then they soak you with shipping costs. Make sure you read the listing carefully to understand what your final cost will be.
Signing up is free and easy. The people selling the goods are the ones being charged for putting their listing eBay so you don't have to worry about that.
If you place a bid and win, you should always follow the instructions for payment. If you win the item and then don't pay, the seller can put a negative 'mark' against your eBay ID (your feedback score is your 'reputation'). You can give him a bad mark too if he sends you a defective product and doesn't try to rectify it. If a transaction is good and everyone's happy, then you put a positive 'mark' on each others eBay id. That's why you should look at a seller's rating before you bid. As a seller, he's looking at your rating too. I always wait until I have the product in hand before putting any comments, positive or negative, on a seller's id.
No flames please but I'm also wary of buying something from anyone who is overseas, just because of shipping time/costs and the number of knockoffs of name brands that seem to come from other countries, especially the far east. That's just my preference, I'm sure there are many legitimate sellers from other countries!
Before you bid if you have any questions at all, email the seller to get more information.
ETA: I forgot to mention payment method. Make sure you understand how the seller wants to get paid. You might have to set up a Paypal account to pay him if he doesn't take checks or money orders.