In order to persuade the electrons in the wire to flow, you need a potential difference between the ends of the wire. Then the electrons will want to get away from the more-negative end and go to the more-positive end. If both ends of the wire are at the same potential, then the electrons have no reason to go anywhere, and they just stay where they are.
The wind-mill is taking kinetic energy out of the moving air that spins it, and uses that energy to do things. It may pump water up out of the ground, it may turn a big stone to grind wheat, or it may turn an electric generator to turn the energy it collects into electrical energy.
It is called "alternating current" or "ac current".
An alternating current is a current the periodically changes direction. Basically, the voltage difference applied at the two ends of the wire / of the circuit is constantly reversed. This means that at some point electrons travel in one direction, then the voltage is switched (i.e. the polarities are exchanged) and the electrons start to flow into the opposite direction, and so on.
