Favourites in TripGo are tied to locations. If you mark a location as your favourite, you will be able to get quick results to go there from your current location. I will also always appear when you search for a location but haven't typed anything yet. You'll typically want to add your home, work, uni or favourite bar or movie theatre to your favourites.
A special case is public transport stops. Those make less sense as favourite destinations. So instead when you add one as a favourite, it'll give you quick access to the next departures at that stop. If you filter that list, that filter will also be remembered.