So which one is voltage and which one is amperage? Is the pipe amperage or is the pressure amperage?

The pipe's restriction is equivalent to resistance. The pressure is equivalent to voltage and the _flow_ is equivalent to current.

You can take this analogy surprisingly far. The same math that is often used to describe and model linear electronics is also used to describe and model a lot of other linear physical systems - it's simply a case of finding the appropriate models for various elements. The water analogy is a fairly simple one.

Here's a simple kitchen experiment that may help you to really get a grasp;
Get an old soda bottle or clear juice bottle, about 2L is ideal.
Find a nail, screw or screwdriver, and put a small hole in the bottle about an inch from the bottom.
Cover the hole with your finger and fill the bottle with water.
Now place the bottle near the sink and take your finger off, and observe what happens.

At the beginning, water spurts from the hole and shoots out a fair distance. This distance is related to how high the water level is in the bottle, which in itself is analogous to voltage. Now watch the water level for a while and get an idea of how fast it is dropping. This speed is proportional to the amount of water flowing out of the hole, ie current.
When the water level is nearer the bottom, you will notice that the spurt is much shorter (lower voltage), but more importantly that the water level is dropping much slower, ie the flow (current) is much lower. The hole (resistance) hasn't changed.
So here you can see I=V/R. As the height of the water level(V) drops, the rate at which water flows out of the bottle(I) drops too. The hole (resistance) is constant.

When your happy that you have a handle on how fast this happens, enlarge the hole and repeat the experiment. You should notice;
1) The spurt lengths are about the same as before.
2) The water level drops faster, ie the average water flow (current) is increased. Note that the I=V/R relationship we saw earlier is still there - the water flow will still be higher at the start than at the end, since V (height) is still decreasing with time. Since the height of the bottle hasn't changed, the range of voltages is still the same. If you marked a line somewhere on the bottle and labelled it x Volts, then it is still x Volts. So the only way that the water flow (I) can have increased is for R to have decreased - and that is exactly what we did when we enlarged the hole.

Play with it a bit and hopefully you'll get it.