We have a want to buy category and a for sale/trade category. If you are looking to buy items, then post in the want to buy. If you are going to sell items, then post in the for sale/trade. Make sure to post prices if you are selling. Posting in any category on the forum is done the same way as any category. Not sure what you mean by directions?
When you block a person, they can no longer invite you to a private message or post to your profile wall. Replies and comments they make will be collapsed/hidden by default. Finally, you'll never receive email notifications about content they create or likes they designate for your content.
Note: if you proceed, you will no longer be following .