How does a transistor amplify a signal?
I always find it easy to understand electrical phenomenon by the analogy of water flowing in pipes. Think of a transistor as a valve in a big pipe through which a large mass of water is moving. Then imagine that this valve is opened and closed, not by hand, but by the flow of water in a smaller pipe. Now you can see how the changes in flow or pressure of the water in the small pipe, by opening and shutting the valve, control a larger flow of water in the big pipe. This is the way signals are amplified by trasisters.
