Motherboard
Step 1. Open your case and lay it sideways.
Step 2. There are holes on the metallic side of the case inside. These are the standoff screwholes which came with the case you purchased. There are standoff screwholes on the motherboard too, count them and remember their position and mirror it to the case so that each stand off fits into every hole the motherboard has.
Step 3. Screw in the standoffs into the appropriate holes in the case and gently slide in the motherboard, making sure each hole is occupied and no extra standoffs.
Step 4. Screw in every hole with a screwdriver on top of the motherboard. Make sure they are all screwed in.
Done