When I clicked on the .jar, instead of launching the launcher, it just opened the archive of files in the jar. I tried to download a second copy, but the same happened.
Do I need to go into Terminal and use sudo to link JDK to the .jar? I really don't know what to do.
type in terminal:
java -jar <name of launcher>
or make a shell script that contains the same.
From your brief description i assume you are not running it on Windows, if you do, ther is a bit difference for that command line, but basicly works the same.