Sellers:

Step 1: If you are a seller, determine your product.

Step 2: Register for a price plan that suits your needs.

Step 3: After you register for your price plan, you post your advertisements.

Step 4: Market your advertisements via signs and flyers (included), email, facebook, message boards, etc.  

Buyers:

Step 1: If you are a buyer, determine what you want to buy (or what you'd like to price)

Step 2: Either browse or search the categories for something specific or just to pass some time.

Step 3: Click on the advertisement that you'd like to look into.

Step 4: Contact the poster for more information or to buy from them.

You can communicate over a variety of ways through the website.  One way is by messaging each user, or another way is to contact them using their posted information.