How do i close my gerber pocket knife?

Somewhere on it there is something you have to push in order to release the blade locking mechanism. If it's a regular pocket knife and not a multi-tool, there should be a little indentation on the back of the blade side of the handle that you press while carefully applying pressure to the back of the blade to get it to fold back up. On multi-tools, the principle is the same, but there may not be a separate, easily identifiable lever to push. The other attachments in the handle recess have to be pushed in order to release the blade lock. No matter what type you have, there is a piece of steel that must be be pushed in or squeezed in order to fold up the blade. You just have to experiment and carefully apply pressure to the back of the blade. If it's old and rusty or new and stiff, it may take a little more force, but it will eventually get easier and you can always add a drop of oil to the pivot points.