This is the Marketplace where the other Level 3 + Up players create and manage their own shops. To create one yourself, your Dragon must reach Level 3. Once you've done that, just do the following.
1) Think of a name for your shop and post a new topic with that as the title.
2) Type an introduction (description, what it looks like inside, etc.) and the items you are selling. Make sure to add a reasonable price.
3) Players will post that they have bought your item(s) and you will have some more money!