I dont know who Arumba is , but is a good see him playing and comment the game.

Nice work on his part!

I'm unclear on how to take a selected group of units and add them to a control group. He has control group one, click-drags more units and then does something that includes the "V" key to tell it to go join control group one autonomously. Can anyone explain that for me?

Thanks!

I don't know what you see him doing, but you can simply move them into the existing group.  Clicking on a unit, instead of the ground, gives you a blue indicator instead of green, and they join up.  Which is what the AI is actually doing when he talks about how they can make control groups with one unit and order reinforcements.

I'm afraid that's not visual enough for me. He clearly uses a lot of keyboard, too, which I don't (yet?) do...

Gonna fire up some skirmish and play around.

OK, I can click on a member of the control group as the destination for the new unit(s) and they join up. I'd swear he's doing that without moving the screen to the destination group, so with the keyboard somehow?

Did you try the control group entries on the left hand side of the screen?  Once you assign a group a number, it gets added to the interface up there and you can click on the units listed in the same way.

Check out the video at 8:40 and tell me how he does that. I can't figure it out.

He says he's doing 1, click, V.

V is the shortcut for form group, he creates a group, hotkey 1, and to add units, he hits 1, drag clicks in more units, and hits V to form the new group under 1.

Which reforms the army. I wish it would act like a reinforcement: form a mini-army of it's own, head for the army, and THEN join...