Question regarding different paragraph styles.

I'm writing something where I need to be able to switch back and forth between multiple paragraph styles all with different indentations and font size. I've tried writing a couple of \newenvironment commands to set the margins, but this doesn't seem to be working. I've also read some online documentation, but none of what I've found addresses this issue directly.

Though, my problem may be that I've only ever used Latex for mathematical papers and never a book. Anyway, help would be much appreciated.