For all you new guys -- glad to have you here!

Don't feel bad about asking questions, even about the most obvious aspects of a knife. No one was born knowing everything. Bladeforums is here for all of us to share and enjoy what we know.
A good place to start learning some knife information is the
BladeForums.com Knife FAQs.
The FAQ has very little on locks, which are a very complex subject in themselves.
slipjoints - no lock at all. Traditional folding knives.
lockbacks - simple, strong, reliable. When the blade opens, it jams against the backspring. Pushing down on the designated area on the backspring releases the lock.
linerlocks - Many folding knives have handles made up of liners, generally metal, and handle slabs, also known as scales, overlaying the liners. In a linerlock, one liner is cut and pre-bent, so when the blade is opened, the liner pushes into place behind the tang (the end of the blade opposite the tip). Pushing the liner back against the handle slab allows the blade to be closed.
framelocks - Imagine a linerlock without slabs over the liners. The liner, cut and pre-bent is exposed, and generally thicker than in a regular linerlock, becuse it is atually the frame of the knife, and therefore stronger. Since there are no slabs, your hand will push in on the lock bar holding the blade from closing, strengthening the locking action.
axis, arc, and ultralocks - A bar rolling back and forth in a slot cut just behind the tang allows a spring action to push the bar to where it jams the tang, keeping the blade from closing. The bar estends out past both handle slabs. Pulling back the bar will release the blade.
There are other new or specialized locks, many off-shoots of the locks above: compression locks, ball locks, rolling locks, bolt action locks.