(adsbygoogle = window.adsbygoogle || []).push({}); I'm a noob to minecraft so I'm wondering when a friend sends me a .class Java file does he expect me to put that in my minecraft folder? and what do you think its for?

Depends on what it is being used for, if it is an additional .Class you may need to get more information but if it is a modified Class file you can overwrite the one you have in the Jar file or wherever else it is supposed to go.

You need to open minecraft.jar with a rar opener, (google it), and then drag the files into the correct directory.