I don't see the term lock buckle in any description of your case, but the only thing I can think of is that it somehow refers to the way that the drive bays rotate out on a hinge for easier insertion/removal. Looking closely at several pictures of your case on newegg that is the only thing that sticks out to me as unique about the case.
That's kind of a cool feature. My htpc case is a hassle to work get things in and out of.
I wouldn't even use the 275W power supply that comes with it though.
I got a new small computer case and it came with from what I can figure is called a lock buckle but I have never heard of it and would like to know how to use it
Case is: Apex DM-387
The lock buckle is an elementary physical security device...a small L shaped metal bracket with a large hole on one side of the L, and a small threaded hole on the other. Inspect your front-side PC cover, the rear edge will have small slot that accepts the buckle. Once you locate the slot, you will notice a hole and slot in the rear plate of the case that aligns with the cover slot. Install the buckle in the case by sliding the side of the buckle with the large hole through the case from the inside. The small threaded hole will line up with a small hole in the case. Screw the lock buckle fastener from the outside attaching the buckle to the case. Slide the front panel into place, over the buckle, and when in place, you are able to insert a small pad lock through the hole to prevent others from quickly removing the case cover to gain access to your PCs vital components.