I used to employ many minimum wage workers so I learned not to overlook things when explaining something. :)
Hey, I should mention, I made a 46 second video with a similar purpose, to show someone on a forum how I was doing something that I was trying to explain. (How to use a tire inflator to remove and replace golf club grips.) Anyway, it now has a huge number of views and I got a check for over $100 from Google AdSense! What a country! I have wondered what else I could do like that, but never have applied myself to it.
Yes, the clamp... you take a screwdriver and push on one of the smaller sized cutouts on the back of the breaker box. Then bend the cutout "coin" back and forth till it breaks off. The clamp goes into that hole. You can tighten it in place simply by holding the nut with your fingers while turning the more accessible clamp on the outside of the box. The nut has a grippy surface and will grab the box. Otherwise, it would be a big fight to get a pair of pliers in there past all the wires.
You'll probably make a mistake or two which you will learn from, but as long as you work safely, you'll get it all working. It's a very nice simple way to do your first electrical handyman thing.