This is a simple mirror mounting system. On the pictures it is shown such that you can see how it works. Normally, of course, the clips are almost fully hidden behind the mirror.
You need to select the appropriate STL file depending on the thickness of your mirror. You need to print the file twice. For mounting, first drill two holes 2cm above the lower border of the mirror and mount the two simple clips. Then drill holes at the upper part and mount the part without the teeth. Finally the mirror is put into the lower clip, pressed against the wall and the last parts can be pressed down to fixate the mirror.
Note again: The pictures show you how it works, not the final result. Obviously the mirror on the image should beshifted to the right such that it hides the clips. (And the clips wouldn't be printed in this awful yellow color that is only good for demonstration purposes.)