It's pretty easy - compared to finding the other party and then negotiating terms and arranging for payment, LOL.
You just call MS - (I recommend a 3-way cal if possible) and make the request. MS does the rest. If you can't do the 3-w, be sure you have all the info you need from the other party. Believe you need other member's name, address and TN at a minimum.
If you haven't already, pop over to the Rent/Trade Forum and read all of the "sticky" threads at the top of the page. Then read a few of the posts and the responses. I think you will get the idea. You are on your own as far as negotiating terms.