Installation of the motherboard is the same as with any case; line up and thread the necessary standoffs onto the tray, change the I/O plate if needed, then screw the board in place. The PC-A12 lacks a removable tray which isn't a huge necessity, but is one feature I wish all cases had.
To install the hard drives, it is just a simple matter of putting four rubber mounts on the drive via four screws, then sliding the drive into place. I really like this system for the fact that it's secure, and also helps reduce drive vibration - hence less noise. If you move your case around a lot and want to make sure the drives can't come loose, you can put an extra screw in to properly mount the drive. I tried to mount the drives in the rack backwards to help hide the SATA wires, but it wasn't possible because there was not enough clearance between the back of the rack and the side panel or front fan depending on what way you had the rack mounted.
To mount external drives/accessories, the front face plates need to be removed. You can either take off the whole front face plate, or squeeze the plates out, but you risk scratching the case this way. Once the plates are out, optical drives are simply screwed into place with no special mounting system as are the 3.5" bay accessories. It would be nice if they had some form of vibration dampening for the optical drives, because they can be one of the noisiest parts, and produce most of the vibration in a computer.
The Power Supply Unit is mounted to a plate that is attached to the back of the case with four thumb screws. The unit can be easily removed without tools if one so needs to do so.
Finished Look
Once everything is hooked into the motherboard and is cleaned up, you'll end up with a nice clean looking system.