Drawer Slides Are Priced & Sold in Pairs Only. Unless expressly stated as being included, screws must be ordered separately for slides.
Sizing of slides: You can safely figure a 14" slide will fit a drawer length up to 13-1/2" and a cabinet depth of 14" to possibly a little more. Usually, the slide is sized to cabinet depth, with an allowance of an 1-1/2" or so. Actually, you can exceed this allowance, using a much shorter drawer and slide, but this combination loses available storage space.