How gravity, the sun, and magnets make electricity:
1) The sun shines on water with enough energy to make it vaporize and turn into clouds.
2) The clouds float around, and then when the circumstances are right they rain down water... with gravity.
3) When in rains in an area with stuff to direct the flow (like mountains), they create rivers.
4) Some creative folks decide to block these rivers with dams to create lakes. This stores a type of energy called "Potential Energy". Its main variable is the mass of the water, the height it can fall and
gravity!
5) Then they convert the Potential Energy into Kinetic Energy by letting it fall through tubes to go through turbines, which spin. See:
Gravity and Potential Energy
6) That Kinetic Energy
magnets between a bunche of copper wires! This causes the electrons to move in the wires, thereby creating electricity.
Illustrations can be found here:
http://www.fwee.org/gen.html
Some benefits with the dammed water is that it can be used for irrigation nearby, and the river(s) can be made navigable with locks for cargo barges. Unfortunately it has turned out to be a bummer for certain fish (there are no salmon on the Columbia River near Castlegar, BC) and its a bummer for white water rafters (places my dad rafted on the Snake River are now lake).
Remember you cannot break the basic laws of thermodynamics:
1) You can't get something for nothing.
2) You cannot break even.
3) You cannot even get out of the game.
An expanded explanation is here:
http://www.physlink.com/Education/AskExperts/ae280.cfm
