The transisitors amplify current. A small current at the base will allow a much larger current to pass between the collector and the emitter. Tranisistors are often used as amplifiers or switches.
For our class we are only going to use the NPN: Which means the middle lead (the BASE) will need positive power to press and start electricity flowing. This is the basis of all computer interatction .
On one side you have the Emitter and the other the collector
I have two examples on the table of how things can work. You can use them to do all sorts of things one thing I like to build is a motion detector.
One motion detector, one NPN transistor, one nine volt battery, one buzzer, one child.