^^^ Grab one and most of your questions will be answered. Basically though, depending on point brackets, you'll need at least one "hero" keyworded unit, and a number of "battleline" keyworded units. Numbers of each vary per points bracket of course. It's all broken down in the GB along with a bunch of other stuff. Other then those initial "taxes" it's pretty open, with the only limits being on huge monsters and arty pieces.
Here's a quick review of it when it first came out. Keep in mind another one is supposed to drop sometime in the next few months they say.
https://www.youtube.com/watch?v=dJL-ZoWj00U