Moosepunch wrote:I have no idea what I'm doing...
First, just to cover every possibility, do you have Java installed? If you don't or are not sure go here:
https://www.java.com/en/download/ You can both let it check if you have it and/or download it from there if you don't.
But I'll just assume you have it installed. If you go to
http://xmage.de and click the download button you will get a file called XMageLauncher-0.3.4.jar. This is a jar file, not a rar, what might be happening is that you're opening it with your rar program (WinRar, 7-Zip, etc.) by default. Put the file in whatever folder you want to have XMage installed and then right-click it and select "open with" and from there find and select Java as the default program to open jar files with.
If you do have Java properly installed and select it right as the default program to open jar files with you should now see the launcher open.
If you still run into problems just post where exactly is it that you're stuck, what you did, what your operative system is, screenshots of the files and errors, etc. to give as much information as possible in one go.