Here is a basic diagram of how the cleat works. The back of the cleat is slanted (usually 45 degrees) leaving a gap between the wall and the cleat. The clamp rack then has a piece on the back of it that fits into that gap and "locks" into place.
I have clamp racks to fit the different clamps that I have. I cut a slot to hold each clamp. Some clamps have a wider neck, so therefore I have different widths of slots depending on what I want the rack to hold.
I made my racks out of maple, with plywood cleats. The slots are cut on the table saw using the sliding cutoff sled that I made a few years ago:
You can also use dado blades set to the width of the slots, but this is just as easy. I mark the width I need the slot to be and then clamp the board to the back of the sled and run it through the saw with the blade at the height I need to make the proper length of slot. I then move the board and run it through again to widen the slot. This photo might make more sense than my description:
As I said, I have a few of these for the different clamps I have:
I also have a rack for my screwdrivers. It is the same basic idea except there are no slots, instead there are holes drilled in the horizontal top piece, for the screwdrivers to fit into.
Another cleat holds my pegboard:
It makes things go smoother when you have a place for your tools and you know where they are. It can be so frustrating to spend time looking for a clamp or screwdriver right in the middle of a project, so I try to put them away after using them. Of course it also keeps things off the floor!
Do you use French Cleats?