...No, it's in a zip file, just open the zip folder and drop the class files into the Minecraft Jar file, to open Jar files you can use a free trial of Winrar or you can use 7zip, then delete the Meta-inf folder that is in the Jar and your done.
P.S. I can't be certain but I think that if you have have a mac you only delete the files inside the Meta-inf folder and not the folder itself, but don't quote me on that cause I can't be sure.
The Beginner tutorials didn't tell you because you have to be pretty far into the game to get into the Nether.
Go to the Minecraftwiki page Here to learn what it is and go Here to learn how to get into the Nether.