To install the PSU, you have to unfasten the mounting frame:

Then insert the PSU into the case, put the frame back in place and then fasten the PSU to the frame, holding it from inside.

That’s just like a chapter from a computer Kama-sutra. If you’ve gone through this operation once, you won’t ever want to do it again.

It’s good you don’t have to use a screwdriver to fasten the drives. Optical drives are secured with special brackets:

You insert the drive, apply a bracket and turn the lock.

HDDs which are mounted into the cages above the PSU use rails:

And if you want to put them behind the intake fan, you should use special guides that adapt a 3.5” HDD for a 5.25” bay.

The assembly procedure is the same as with an ordinary system case, making allowances for the “upside-down” design. The mainboard goes in without problems: