They change the gears on a automatic bike to put it simply

Bicycle rollers are a way of riding a bike without going anyway, they are generally used for training and exercise - unlike alternatives you actually have to balance, this gives many advantages. Say you don't like the outdoors, or watching Tv in your own home whilst ridding a bike appeals to you, then you will find bicycle rollers an excellent substitute for well the road.

In the variator. Take off the belt cover, and its the wheel on the left or toward the front of the bike.

If you mean stabilizers that you attached to the back of your bike to keep you stable the answers yes. As stabilizers stop you from falling over keeping you balanced.

You can buy something called a "trainer", which attaches to the rear wheel and lifts it off the ground. With that, and a phone book under the front wheel to get the bike level you're all set to use the bike as a stationary bike. There's also a contraption known as "rollers", where the're is a frame with some rollers in. The rear wheel sits on two rollers and the front on a single roller that's powered by a drive belt running from the rear rollers. This gives a bit more road-like feel to the riding, as it requires you to balance your bike just like on the road.