Like, what all the commands do in combat, and how combat even works....

That has been a complaint since the game came out. Back in the day, games cost a lot of money and you generally didn't have very many. So a huge gameplay desire was for the gameplay to be cryptic and require experimentation to just learn how to play. Of course, that sort of gameplay is hated these days.

So, you can:

A) Experiment like the good ol' days.
B) Get a walkthrough (Gamefaqs has a decent one) and read the beginning that talks about what commands do. Even so, you'll find yourself experiementing.

I honestly can't remember much of anything of 3. I played 2 for a million hours and I only brushed up against 3 before moving on to the later games. Hopefully, someone can give you some more hints if the walkthroughs don't help.

Combat in Might and Magic basically follows "stick them with the pointy end", meaning clicking with the mouse. The command for shooting an arrow for party members with bows is "s", casting a spell is "c".

At first, I too was perturbed at the lack of information pertaining to the mechanics of the game both in game and in the manual. But then I just said F it and learned to enjoy the "abstractness" of it. Just remember that bigger blood splash = more damage and check the hint guide that comes with the GOG version if you get too frustrated.

In addition to the rather useless manual (it feels more like something you would get with an Ultima game) there should also be a reference card that explains the UI and the commands. The "manual" is just fluff, it's the reference card that explains how to play the game.

You can also read the manual of MM4 or MM5 (World of Xeen), the commands are quite the same.

In addition to what petrus and kmonster mentioned, you can also visit the rpgclassics might and magic 3 shrine for some good info.

http://shrines.rpgclassics.com/pc/mm3/general.shtml

The general info and character creation page provide just about everything a proper manual should. I found in pretty invaluable when starting out in MM3. There's also a walkthrough and bestiary section but you can just ignore that if you don't want any spoilers.

Thanks for all the replies guys, much appreciated!

I'll check the rpgclassics link and the MM4 manual.