This is not a responsive modile theme, no - it's best suited for desktop browsers. Ads are just regular Drupal nodes. Users would just be granted permission to create them as they would with any other Drupal content type. If you're new to Drupal, it would probably be best to download and try Drupal first, since there can be a bit of a learning curve for new users. There's a variety of concepts that could be kind of overwhelming if you're jumping right into administering a complex site.