I have a wall in a room that's hardly used I would love to add shelves or cabinets
What about floating shelves! So easy to diy build: https://www.charlestoncrafted.com/how-to-build-and-install-floating-shelves/
To what purpose do you now put this room? Is it for overnight guests? A sitting room, a craft room, a t.v. room? That would first determine the kind of shelves or structures you want. We just pick up odd book cases we come across (I have one near me. . . a bookshelf, jammed with books, which is on the radiator) There is also a very small bookcase nearby, also filled with books. A book case with glass doors is a special and good way to display items besides books, If you want to display items individual shelves would be nice.
You might consider doing an Ikea hack if you don't want to build the shelves yourself. The Billy bookcase is one that people often use to create built-in-looking shelving. They line them up, and then add trim around the edges to connect them together.
On the empty wall in my house. First, I measured the length of the wall that I was going to use. Secondly, I went out to the HOME DEPOT and bought some white shelves and brackets, (Like the ones that's you see in the closet or pantry). Thirdly, I attach the shelve rack about 2 feet or less from the ceiling.
I used the 'L' shaped brackets to hold the shelve racks. the brackets also have the screws that you will need. After the shelves, I mounted a flat screen TV on the wall. It looks great