Rails (or ribs), are narrow strips of plastic or metal that are attached under the deck lengthwise along the edges. They are used for additional grip for grabs, and to enhance sliding while protecting the deck's graphics at the same time. Rails also provide a more consistent feel for slides, as the slide of a regular skateboard will suffer from the wear of the paint or varnish on the bottom of the board. Although rarely used anymore, they are useful for experienced skaters that are capable of grabs.
To get higher ollies, I would suggesting resting your back foot on the very end of the tail and the front foot in the middle of the deck to allow for more slide. Popping as hard as you can and catching your board in the groove of the nose with you ankle practically resting in the groove will level the board out in the air. after this initial movement slide you feet back to the bolts on the tail and nose to ensure a clean landing.