system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do you store energy/electricity?

If i were to build a dam in a river, to focus the flow of the water and try to harness it. I guess i would create some sort of wheel that would be spun by the power of the water. How do i turn this into energy and eventually even store it?
gpt
Imagine you have a long line of golf balls, all touching and side by side. This is a wire, lets say its a copper wire because copper is easy to make into the long wire and its something the imaginary golf balls have an easy time rolling in (it could also be made from steel and some other metals). These golf balls are electrons,   a metal, like copper, is an element whose electrons can "move" around. 

If we push on the balls without them rolling (imagine on the other end something was blocking the way that will move if you push hard enough) we have just created Voltage, its the pressure pushing on the electrons. If they move we have Amperage, the number of electrons that move or flow down the line. How hard we have to push is the Resistance.

Now, we can't just push the golf balls into nothing, that would make empty spots in our line and it wouldnt be a line anymore. So imagine the line goes off into the distance and comes twisting back around so that the other end is touching our starting spot. Now you can see that by pushing the balls forward they will roll like a train and fill up the spot where you moved them from. This is the flow of electricity, electrons move out but simultaneously move in from the other way. We could say the direction they go is positive and the direction they come from is negative.

Now let's create some power. Magnets, or actually the magnetic field magnets make can gently push on those balls without touching them, very useful! If we spin the magnet we can push one ball forward every spin. This is nice but its not a lot, so let's take our wire, the long line of balls, and wrap it around outside the spinning magnet many, many, many times. Now when the magnet spins it can push alot of balls at once and with a lot of pressure. We need a way to keep the magnet spinning, we could do it by hand but that isnt a real job. So lets hook the magnet up to a big fan and spin the fan. We could use wind, or steam (coal, gas, nuclear all heat up water to make steam to push the fan to turn the magnet) or we can use flowing water. We could also make a special type of wire that makes sunlight move the electrons but we can focus on the basics.

Now we have a big spinning magnet and lots of wire pushing electron and creating electricity. We can do way to many things with it for me to cover everything, but ill be happy to answer specifics. As for how to store it, we can use batteries. We actually use so much electricity that our magnets are practically spinning all the time, but sometimes we need batteries. There's many types, but the basic idea is to take two different metals and submerge them in an acid. The acid has holes in it that want to be filled with electrons and the two metals have plenty to give. So if we add electricity to the battery it will "charge" and fill up all its spots. We can then take electricity from battery by connecting to it later. The actual number of electrons in the battery doesn't go up or down they just change locations from the acid to the metal and back.