Buying a good quality case is sometimes over looked. A good case is generally heavier and made from better metals, blocking external interference and providing better airflow, internal design with easier access to the components.
How to build a PC
To start building your new PC the case will need to be opened. Depending on the type of computer case there are usually screws located on the back of the case. Once the screws are removed you can slide off the cover.
With the cover off you should be able to see some holes on in the wall/floor of the case. These holes are where you will need to screw in the supplied motherboard posts/supports. Some cases may have supports already built-in or installed.
Note: You need to make sure that you screw in the supports so they will align with the holes in the motherboard.