A turbo is one of the most popular ways to add hp. You should understand exactly what each of the components do. To understand this ypu must first know the basics of a turbo. Here are a couple of good sites that will teach you this.
Basics of Turbo:
http://auto.howstuffworks.com/turbo.htm
http://www.turbobygarrett.com/turbobygarre...bo_tech101.html
Now these are only the basics and the componets. There is alot more to it than this. I find that garrett really does the best job in explaining the intricate details. So here ya go
Advanced Turbo:
http://www.turbobygarrett.com/turbobygarre...bo_tech102.html
Expert Turbochargers:
http://www.turbobygarrett.com/turbobygarre...bo_tech103.html