Pizza stones are porous clay platters which help retain heat and place it right next to the crust. This results in better pizza than you can usually make in conventional home ovens (which are not as hot as commercial pizza ovens).
Pizza stones are similar to cast iron cookery, they get better with age as they become more seasoned. You should put a thin layer of oil on a new stone and heat it so the stone becomes more smooth and less likely to stick to the pizza. Never soak your stone in soapy water. Never put a warm stone in water or it can crack. I received my stone with stand as a hand-me-down from somebody who left the area in a hurry. I felt lucky to get it fairly well seasoned and I am guessing that it is probably between 5 and 10 years-old.
This is not a commercial grade baking stone, and I am sure that it will crack someday. Actually, I feel lucky every time that I use it and it remains in tact.
The stone must be preheated for a long time (about 45 minutes) to get it up to temperature. Make sure that your dough, sauce, and toppings are all conveniently staged. When you remove the stone from the oven, use the stand or other heat retardant surface. If your stone is not well seasoned, throw a bit of cornmeal on the stone to prevent sticking, then put the dough on the stone. If you have a pizza peel, your pizza can just be dropped on the stone. Otherwise, you can work quickly to add the the sauce and toppings to the dough on the stone and return it to the oven.
This 15 inch stone also works well with Take-and-Bake pizzas. It will keep anything on top of it warm for a long time. Some people use the stones for cooking pastries or cookies. I think my stone might impart the flavor of garlic and anchovies.
I don't think you can go wrong with a pizza stone as long as you take care of it. I would not buy a really expensive one. I am very happy with mine. I just hope I never drop it.