Bicycle Mechanics - Simple question concerning sestpost clamps

I've always ridden bikes that had seat post binders integrated into the frame. But these seat post clamps... I'm curious. How do they work exactly? I feel like the answer should be obvious enough, but I just want to be absolutely certain I understand this piece of equipment.


I'll just type out everything I'm thinking here...

Where exactly are they attached? Not to the seat post alone; that wouldn't bind the seat post to anything and the post, while unable to fall into the seat tube, could be pulled right out.

Is it attached in such a way that it overlaps the seat tube and the seat post, but with a ring added around the seat post in order to thicken it and allow the post to be held with the same tension that is binding the clamp to the seat tube?

Or do seat post clamps simply squeeze the top of the seat tube which then prevents the seat post from moving up or down?

I found a few threads on here regarding which seat post clamp size to choose in relation to the size of one's seat post, but I couldn't put my mind at rest concerning, like I mentioned above, how exactly clamps function and where they are placed. I searched and searched but I just couldn't be sure.

So what's the deal?

I have aluminum frames; seatpost clamps simply squeeze the seattube (which is notched in the back) to hold post in place. The clamp should pop onto the top of the seat tube with 1mm-2mm of clamp above the top of the seat tube. Often clamps have a bit of a flange around the inside of the top lip so its impossible to slide them down far enough for the clamp lip to be flush with the top of the seat tube.