You use a pre-amp when you have a mic that doesn't have battery power and your plugging into something that doesn't provide power.
Some recording devices have "Phantom power" that provides power for standard mics.
You have these a bit mixed up:
Phantom power is a power source for condenser Mics, they require power as part of their design though some have batteries as well.
Dynamic Mics do not require any power.
Note: Only use phantom power on things that need it, otherwise you could end up frying things!
Pre-amps are for everything. It's the first thing a signal goes through when it goes into a mixer. You use them to increase the level on Mics (all types), guitars and anything else (even synths if they need it).
All Mics will need to go through a pre-amp whether it has phantom power or not.
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I'm learning a lot of this stuff at the moment as well but there's a lot of help out there.
Youtube has loads of stuff.
There's a free book here on setting up a studio:
http://www.recordingreview.com/killerhomerecording/KHR_SettingUp.phpProAudioDVDs.com have a weekly free video.
They also have a DVD set called "Ultimate Home Recording School". Bit expensive but very good, covers a lot of the basic knowledge you'll need.