What does Base do? Does it control current or voltage?
Someone once told me, when I was first learning about bipolar transistors, that a transistor was similar to a faucet. The tap itself was likened to the collector (on an NPN) and the sink (not talking about FETs here) is like the emitter. The base is like the knob that "turns the flow of current on and off." That is to say that if you have a little bit of voltage going into the base of the transistor, the collector and emitter are connected electrically. This was the simple explanation I got when I was a kid. Though it is actually a little more complicated than that, it did help me to understand basically what a transistor did.
As for the p-section between the two n-sections, it is actually relatively easy. I don't know how much you know about chemistry, so I'll try to make this simple:
If you look at a periodic table of the elements, you will see silicon (#14) in the group 4A, meaning it has four free electrons that are not bonded to anything. Therefore, when several silicon atoms are bonded together, they form a lattice design, as in the picture below:
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There are no free electrons to move around, and therefore, current cannot flow. To make the semiconductor work, the silicon must be "doped" with another element that has a different number of electrons. To make the n-section, phosphorus or arsenic are often used. These elements, as you can see in the periodic table, are in group 5A, meaning they have 5 non-bonded electrons. When silicon is doped with phosphorus or arsenic, four of the electrons bond, but the 5th ones remain free:
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*Note: sorry about the huge picture
Because of the free electrons, electricity is able to flow.
For the p-type section, silicon is doped with an element from group 3A (three "extra" electrons) such as boron or gallium, so when bonded together, there is a "hole" (where an electron could be):
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As you can see, there is one electron less (next to the boron atom). In an NPN transistor, the p-doped silicon is used as the base. When a little bit of electricity is applied to the p-section, the hole fills up, and the current can flow through between the two n-sections. This link may also help:
https://www.elektropage.com/default.asp?page=cat&cid=2&tid=27
I hope this helps, and let us know if you have any more questions!
Der Strom