I have never done this before and I would like to know how I can also make sure I don't get ripped off
Basically, you make a thread that denotes what you need, and people will reply to it and you send each other Private Messages and work out a deal. Then you just exchange shipping info and send the cards on their merry way! Or you could post on someone elses thread or even just PM them and skip posting on the thread altogether.
Really, there isn't a surefire way to make sure you don't get ripped off, but just check the "Trusted Traders" post that is stickied at the top and see if the person you are trading with is on there. If not, then it is a "leap of faith" deal.
You may want to start with some small trades to boost your confidence. There are a lot of trusted traders on this forum I suggest you start with some of them. Shipping is an issue you might want to think ahead. Most people send a hard sleeve to protect the card or cards. Depending on the number of cards you send a regular envelope should suffice. Of course if the cards are more valuable then a bubble mailer or padded envelope is nice. There have been reports of envelopes been ripped and the cards falling out, so I suggest that the cards be wrapped in a piece of paper to reduce wear on an envelope. I have also found it nice if you send a list of the trade with the cards and your user name to help with confusion.
Any other problems feel free to pm me and I'll try and help the best I can. Rasser