Case

 CASE 

All of the components of the computer are housed in a stylish box called the computer case. It features pre-defined sections with screws and holes where all of the parts are meant to be positioned and fastened, and it can be opened and closed.

PC cases vary in size, color, and fan configuration; some have glass side panels, others don't, some have RGB lighting, and some have quite bizarre designs.

To put it another way, a PC case is a box that is either colored or black and has buttons on top. All other components required for PC construction will be installed within the PC's casing.
Another option would be to just place your components on the wall or spread them out on the floor; some people do, but it's convenient to be able to simply take up the entire computer by lifting the case.