Welcome to Bladeforums!
See the FAQ for Bladeforums rules at
http://www.bladeforums.com/forums/faq.php
Paid memberships at
http://www.bladeforums.com/forums/payments.php
Exchange rules at
http://www.bladeforums.com/forums/announcement.php?f=699&a=98
You need a Basic membership to post a trade thread,
a Gold membership to sell what you've bought,
a Knifemaker membership for what you have made,
or a Dealer membership if you sell for others.
Once you pay for your membership, go back to Paid Subscriptions to see when it takes effect. PayPal costs more and takes longer to go through. Credit card payments are automated.
Then go to Settings (upper right)
then to Permission Groups (left side)
then select your correct membership level.
I suggest browsing the FEEDBACK forum at the top of the Exchange, especially the stickies, for problems to watch out for. Browse the forums you are most likely to post in or buy from:, Dealer, Knifemaker, or Individual, to see how members communicate.