find the wall you want your shelves measure so you know how many boards you will need. go to your hardware store and choose your wood you will need screws a stud finder with a wire finder if you don't have one but not required
Take a stud finder and go to the wall where you want your shelves.take the stud finder and find the studs make sure there no power wires where you are cutting.now measure your space between the studs and take in account the width of your board and cut
now take and screw your shelves in what how far you want them.after you do that it looks like a book case.
now go to the wall where you cut out and slide it in and screw it to the studs and fix your trim or what ever you want to decorate it.