Incoming longpost is long.
Oolrich wrote:
I'm looking for advice on how to actually DM, specifically how to decide NPC actions (mainly in combat) and how to properly nudge the party towards the goal.
There's not enough room here to go on and on about it, but the key for NPC actions in combat is: don't be afraid to play enemies as smart as they are. Animals are going to rush into melee, maybe use minimal pack tactics. Orcs are militaristic and might know several battlefield tactics like flanking, but ultimately default to their innate strengths, which are... Strength, as in brute force. But the evil wizard? Int 18 is like genius level. That guy is going to have contingency plans. What to do to fight melee guys. How to fight other mages. Figuring out who the healer is, and targeting that guy. A smart enemy with plans is a challenging enemy, and a more memorable encounter overall.
Playing enemies in ways that match their intelligence makes fights more interesting. If every enemy just runs in close to melee your party, then your party will adapt tactics that only cover that situation in battle. If you're afraid they won't react/know how to react properly to a situation you're setting up later, give them a small scale version first. Like, if you think they aren't ready to face the long-range wizard, give them a fight against a low-level elf sniper up in a tree. If they struggle, they'll learn from it and hopefully adapt. If they ace it, then they're fine.
As for nudging toward goals, most players are keen enough to understand the DM's hints that "the story is over this way." If not, just make everything Schrodinger's plot. If the dungeon you planned is in a castle, and the party wants to explore the woods, surprise: they just found an abandoned castle in the woods. If you do this all the time, players might become dissatisfied, but using this tactic as you're learning how to DM is fine.
Oolrich wrote:
Also how do you keep track of what all these things MEAN
If you mean game terms, then it's nice to have a player or two who knows the game and can help you adjudicate as you play. Most people are nice enough to want to help out (and not be jerks about it, either). If neither you nor your players know the terms, you can learn them all together. The DM has more responsibility to know the rules basics but not so much that everyone else can't help out.
Here is a good resource for learning some of the game terms:
http://www.d20pfsrd.com/basics-ability-scores/glossary