Changing and declaring fonts for parts of the document without changing the default

This might be a silly question, but I am very confused of how to declare fonts for only one sentence/paragraph.

The solution I found was to use {\fontfamily{ppl}\selectfont ... } However, I am not sure, what excactly each of them, i.e. \fontfamily; {ppl}; \selectfont are, and moreover, what packages I need to call before \gegin{document}.

Moreover, I am now writing a report, for which I am using the package arev, i.e. \usepackage{arev}. So, if I now use a different fort package, it would remove the "arev-default" in the rest of my document, right?

Could anyone please resolve my confusion?

Thank you!

• *\begin (instead \gegin) of course – Fraenzine Nov 28 '18 at 18:14