Gussy - check out the APS website at
http://www.stamps.org/index.htmThe circuits are books with stamps being sold by members. You get a box of the books once a month or so. You buy the ones you like and send the box on to the next member. You get to see what you're buying and the prices are usually competitive. You can also buy from the online stamp store. The material in the store is usually a little more costly, but the quality is generally higher as well. The other benefits are shown on the website. One of the biggest benefits is that you are supporting the hobby by supporting the APS!
Zaro - your application has to go through the process. Your name is listed in the journal in the month after you reply. If there are no member objections, then you are accepted. Your APS membership number is as good as gold in the industry. The process is a method to keep deadbeats out of the society.