I have already built my Military Academy, but how do I make the actual squad?

Go to your groups, make a new one and name it The Mighty Terminators or whatever.

Put four beasts in it.

Go back to your pets page, edit the group.

There's a button that says Upgrade Group to Squad.

It should tell you stuff like this on the Tactics FAQ under the Help menu.

I also made a quick and dirty guide to getting started on the battlefield under Player Guides in the Forum.