A regular 2.5" SSD would fit in the bottom left. Obviously not an M.2 or PCIE SSD.
It's not rocket science to put it in really. That piece is used to secure the SSD/HDD in place. Again, it's not rocket science so you should be able to figure this out on your own.
FYI, a regular HDD is 3.5" and you can't fit those in there.
