You need to be logged in to post to the forums.  If you don't have a login yet, you need to register first.  Both, "Registration" and "Login" links can be found in the top right corner of the page.  Registration and use of the WindsurfPA forums is free.

In order to post to a desired Group and Forum, like "Classifieds - Gear For Sale", log into the site, click on the Forums/Gear page, scroll down to the segment of the page that reads "Gear For Sale" and click on the link.  Then use the "New Thread" button and edit your message in the editor.  To post the message click "Update" link at the bottom of the page.

Once your gear has been sold most users re-edit their forum root thread and add a - SOLD phrase.