Some cases require the use of brackets that attach to the sides of the drive before placing them in the case but most just get secured by just using a couple of screws. Just slide the drive into the case and with the bracket system the drive will lock into place. Otherwise as you see in the example the drives just screw into place.
The drives sometimes need to be aligned with the cases front face cover so that they sit flush once the system is put together. This is easily done by putting the face plate back on and finding the proper pace to secure your device.