You have two ways to manage your multilingual site.
If you just want to translate your categories, use special language files to translate. For example, rename "Cars" to "adsmanager_cars" then look in the translation file for a corresponding entry and enter a value for each language.
If you have everything to translate or if you don't want to do it manually, you can install FaLang (if your Joomla Version is newer than 1.5) or Joomfish on the Tools tab and follow the FaLang or Joomfish documentation.