We've gone as far as we can putting components on the motherboard before putting it in the case. It's time to marry the case and motherboard.
When you unpacked the motherboard, it came with a thin 1 3/4" x 6 1/4"aluminum plate with a bunch of stencil like holes cut in it. Sometimes the holes are labeled. The aluminum panel has one side of the plate with a raised, curled border around the edges. This snaps into the back hole of the computer case, the holes correspond to the ports on the edge of the motherboard.
You want to orient the motherboard so the ports on the edge of the motherboard will be toward the back of the computer case, but first the panel. The aluminum panel mounts from the inside of the case. You'll find that the raised rounded, curved side of the panel will snap into the hole in the case. But first orient the panel so the holes are aligned with the motherboard ports, and then snap the panel into the case. You'll find the panel snaps in place like a soda paper cup lid.
Next the motherboard slips into the case against the aluminum panel. The aluminum panel has small strips that are around the holes. These go around the ports of the motherboard. Make sure when you slide the motherboard in to the aluminum panel ports that there is no metal strips in the way of using the ports.
Make sure there are no wires between the board and the bottom of the case. They should be above the motherboard.
If you look closely at the nine holes going through the motherboard, you'll find they align, or almost align, with the copper stand off posts you put in the case earlier. In the bag of screws that came with your computer case, there are at least nine or more Phillips screws with flat polished heads. Get out your trusty Phillips screw driver and fasten the motherboard to the case by screwing nine screws through the nine holes in the motherboard and into the top of the copper stand off posts. The screws should be tight, but not super tight.
Congratulations, your motherboard and case are one.