These are all good questions. A weather head is a weatherproof electrical service point for your overhead electrical service feed. The weatherhead connects to the top of the electrical service pipe and has a cap over the connection frame. Since it sits atop the pipe, has a cap on top of it, and makes the connection weatherproof, it is called a weatherhead.
The weather head is connected to the pipe with a bracket, complete with two screws, that encompasses the pipe. The wires that feed the electric meter feed up through the pipe and come out of the weatherhead access holes. These holes are facing downward at an angle so that the rain cannot run into the holes. These wires are what the utility company connects their feeder wires to. There are different sized weatherheads, depending on the size of the electrical service and wire size.