To use YouTube you will need know or set up your channels name. The easiest way to find it is to log in to YouTube and click on 'My Channel'. If you don't have one you will be asked to choose a name. This is the name you can use in Favs then. It is also part of the channels URL, e.g.
While logged in visit the following page to see your favorites: Please note that your Favorites are not the videos you 'liked'.
While logged in visit and check the "Favorite a video" setting.