there's a little bit of a learning curve to it, but as the game goes along you'll get the hang of the combats, and it'll be easier as you gain more skills, though some combats can always go sideways pretty easily.
I'll give you a few general tips that might help out until you're more familiar with it
be judicious about which fights you get into --- the arena, for example, is not required to progress, so maybe put that on the backburner until you make a little more progress.
if you mouse the opponent you can see their level, and if you right click them you can examine your opponent, which may reveal a bunch of useful info.
this examine ability is based off your lore skill, I believe.
also, if you hold down shift key, I think it is, you can see the vision cones of stuff you encounter -- avoid these if you want to avoid a fight with some enemy.
walk around and explore a lot, and talk to lots of ppl for all kinds of quests to get ez xp and rewards.
I understand some ppl aren't all that crazy about the talking side of it, but fort joy is like an incubator, and once you level up a bit and escape there will be about as many fights as you choose to get into, so for now explore around and build.
persuasion skill may be useful for some dialogues, and wits help you find hidden stuff.
as for healing, etc, I think maybe it's alt key that shows you items that can be picked up -- red items have owners and are considered theft to take.
grab up all these mushrooms and herbs along the way so you can put them in potion bottles to make your own heal potions, etc.
various books provide recipes or you can experiment.
also, there is a lvl 1 hydro skill called restoration and a lvl 1 huntsman skill called first aid you can buy at the various skillbook traders that will heal.
fortify is lvl 1 geo that bumps physical armor, and lvl 1 hydro armor of frost helps magic armor.
conjure incarnate is a good summoner skill, and warfare has a couple useful skills that can knock down opponents.
what you want to do in combat is id the lower armor on your opponent, punch thru that and then cc them with some ability.
if you're worried about allocating a point to some skill school you won't want later, don't worry about it.
once you leave fort joy you can respec your points all you want for free.
also, I would say get familiar with the various elemental interactions on the battlefield.
ie some surfaces/clouds will ignite, barrels can explode, water will stun a shocked opponent, oil will slow, etc
oh yeah, also make sure to drag all these scrolls, grenades, special arrows, skills, and all that down to your quick bar at bottom of screen for use in a fight.
shields can be very useful, and provide that 'shields up' skill, and if you just have a weapon in 1 hand with the other hand free you will see a punch ability in your bar that can knock down.
