Fantstc1, I just learned this a few days ago myself, so I sympathize.
Add at least one T2 unit to an army, and when that army is selected, you will notice that the Build button is active. Click on that, and you will see that each buildable unit type is available. If you click on a unit type at this point, it will add a +1 next to the same type in the army unit list. You can also shift-click to get +5 or +6 or whatever at a time added.
What I've done in my last few solo battles since learning this is: create two or three armies using output from my first 2 land unit factories. Take over some metal nodes. As soon as I can build a cruiser factory, build 2 or 3 cruiser units. Once I have 2 or 3 cruiser units, click on one of them, shift-click one of the armies, hit V to join the T2 cruiser to the existing army, reset the control group (thanks bug!), and then go in and request reinforcements. I'll click add reinforcement units in numbers that I'd like to see in the final army.
I'll do this with each of my first two or three armies. In a short time I'll have two or three armies at full strength.
Once you request reinforcements, any factories with free production capacity will start building units to fulfill reinforcement requests. This means you don't ever have to go back and manually have factories build things anymore, though you will have to go back and turn off a predefined build queue and the repeat option. Just click or shift-click unit types in the build menu on your existing armies, and let the factories automatically fulfill the requests. It's quite nice, and it's about halfway to where the game really should be (army templates that you can define and instantiate without having to use existing armies and join them into an army).
