Measure the height and length of the space between walls with a tape measure so you know exactly how much space you have to work with. Plan on leaving at least 6 inches of space on either side of the cabinets to prevent damage to the wall.
Compare the size of the wall space with the size of available cabinets. Depending on the available space, you might be able to fit several cabinets next to each other if they can open without interfering with each other. Or, you might have to center a single cabinet in the middle of the wall gap. Ensure the cabinet won't hit the ceiling before you bring it into the space.
Slide your cabinet or cabinets into the space between the walls with a dolly. Center them so they have an equal amount of space on each side so the appearance is uniform.
Fill the cabinets with items you need stored. If the cabinets have glass doors you can see through, decorate the interior of the cabinets with photos, crafts or other decorations.