3) Motherboard
This is the most complicated bit. Before you install the motherboard into your case, you need to fit the separation screws that came with the case into the small holes on its inside wall - sometimes they're small brass plugs, other times they're squarish clips. These stop the motherboard from touching the metal case and short-circuiting as a result. You'll need to match up where on the case the small circular holes on the top of the motherboard will overlay, and stick the separators into those. Next, you'll find a flimsy metal rectangle in the motherboard box, with a bunch of holes cut out. This is for the various mobo sockets to stick through, so it needs to be aligned correctly in the matchingly-sized hole on the rear of the case. Then, gently squeeze in the motherboard so everything's snug in place, and pop some screws through its circular holes into the separators below.
Peering intently at the manual for reference, you'll then need to attach the various small wires from the case for the power and reset buttons and all the various LEDs and fans. And your USB ports. It's a stupidly fiddly business, so have patience.
