There are so many configurations of cases, it would be impossible to cover them here. Many of the newer cases allow removing just one side needed to gain access to the working side. Usually the clue is one or more screws on the rear of the case. The other area of Hardware installs is External parts. Like Printers, Scanners, Cameras, Zip drives, External CD's or other equipment.
Most hardware is Plug and Play install, but there are still tricks to installing.
I'll try to give some guidelines here, but again, there are so many cases, it will be hard to cover them all. I'll cover those that I've had experience with. First, when purchasing hardware, always buy a boxed kit with the software. If you buy an OEM version, it may not include software or instructions. These are parts purchased in quantity for a knowledgeable tech to build a new computer from scratch.