Thank you. That was very helpful. I did that and it worked. For any other newbs, don't forget to make sure you're running that command from the same directory as the .jar file. For example, if you've put the jar file on your Desktop, you need to run "cd Desktop" from the terminal before running the "java -jar forge-1.15.1-30.0.41-installer.jar" command in terminal. I forgot that step and was wondering why Java couldn't find the jar file when I was looking at it on the screen! ?