I own a PB-100 and have been using that as a boost for when I play lead parts in songs.

Is this the proper use of a pre-amp? I'm not even sure what it does. Would I be better off with a distortion pedal? Whats the difference?

Depends on the amp. If you have a valve amp then running a boost out front is a fine way to do it. That drives the valves into clipping so you get distortion from them.
On SS amps this does not usually have a desirable effect. So what one does is get a nice distortion pedal and get your distortion from that. There are some nice ones out there, with many they can also double as a clean/ish boost as well.
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