Configure the Site
As administrator you will always have a menu option that no one else will see: it is called "admin" and is at the far right of the classifieds menu bar.
The admin function has several sections. The first is called "general", where you should set the basic info for your site. The second is "category", where you will choose the categories for your readers.
It is fairly important to configure both these sections as soon as you can. Almost all these options can be changed later if you change your mind, but the classifieds will be less confusing for your readers if you set each option.