Don't worry, feeling overwhelmed by the fighting is a common occurrence. For myself, it just took a really long time of doing it. I still only auto fight, as I just don't have the time to slug it out on the virtual field. If you are in a fellowship, ask them what troops they use for a given province or combination of baddies.
One tip that I have found very useful is that you are better off 90% of the time using five of the same troop rather than mixing different ones in any given battle. It seems weird, when they have different strengths and weaknesses, but that is how it goes. So find one that is strong against at least half of the baddies and select that one for all five slots.