Update: I picked up four of these yesterday and they work perfectly for my application. Wouldn't recommend this thickness / finish for any larger sizes due to support concerns but for my 10" wide and 12" deep little lighted nooks these work great.
This specific glass is annealed. If you are looking for some tempered, or thicker glass please contact your local The Home Depot store and they can assist you.
You will be lucky if your first cut is just right. With that in mind you can find a video on YOUtube showing you how. Once you know how much pressure to put on the scoring tool it looks SOOOOOO easy.