When user pay for promote his ad, where in the site it will be promote? In the bar bellow header? or promoted ads will be posted in the top of list?

The promoted ads will be listed in the top of the list in that category...

Hi,
and how long, ads will take place as a "Top Ad" ? Thanks !

The ad take place as "Top Ad" till the it expires where expiry date is controlled by the admin.

Thanks for answering so fast ! How many "Top Ads" will appear. In your demo site, I've seen 7 ads. If more than 7 are "Top Ads" how it works ?

You can have any number of top ads, there is no limits (but latest top ad will listed first). The top ads will be listed in top of all free ads in its category.