To install you must remove the drawer and bottom of drawer. These will fit on the inside of the drawer. Screws are not provided but are set to use countersunk M4 sized screws.
Quantity of 1 = 1 pair of braces. You typically just need a pair, but depending what you store having 2 pairs per drawer will give it some rigidity. Please be aware DO NOT overload the top drawers as they could tip over,