This will probably be redundant for some of you, but basically, the clamp has a cylindrical portion and a flat portion on the "gold-colored" locking lever. Usually you will slide the mount forward on an AK's side rail (with the lever facing backwards) and lock it in place by rotating the lever forward. The cylindrical portion of the mount's lever locks into the cylindrical portion of the side rail:
When you slide the mount in place, you may find that it is either too tight or too loose. It should lock in place with firm hand pressure ONLY and not be "rattly" or otherwise move when locked down.
If it is too tight to lock down, or is so loose that it rattles, you will have to adjust it. The process is simple if you go slowly and carefully, but it does usually involve trial and error and several attempts.
Only when the mount will lock down with firm hand pressure and is not "rattly" can you consider it adjusted to your individual rifle.
Rather than repeat it here, there is an excellent set of instructions on Tantal's website:
If this is the scope mount you have (note the simplified locking lever), the adjustment does not involve removing any pieces and then reassembling them. You simply turn the mount upside down with the inside facing you. Push down on the movable locking block, removing spring tension from the retaining nut. You can then tighten or loosen the retaining nut until the mount is tailored to your rifle. When you have the squeeze block adjusted properly, make sure that the "tooth" on the underside of the squeeze block locks into the corresponding notch on the adjustment nut. The nut is ringed with locking notches, so choose the one that makes your mount tight enough to require firm hand pressure (but hand pressure ONLY) to lock the mount to the AK's side rail.
This mount uses a simple "squeeze" method of tightening and does not involve anything locking into the cylindrical groove on the AK's side rail. Some people consider this mount therefore to be slightly inferior to the more complicated type, because it is probably more prone to loosening and may require more frequent readjustment as the "squeeze block" wears or shifts under recoil.
(If I can find some good photos of the inside of the mount, I will post them at a later date; I searched several websites and couldn't find any shots of the inside of this type of mount).