When I try to open the JAR file so that I can finish downloading the mod, this pops up: "the java jar file quark-r2.1-233.jar could not be launched"

I am on mac and I have the latest version of Java installed, I'm trying to download quark for 15.2 and I also already have forge installed for 15.2. How can I fix this so that I can download the mod?

You're not supposed to open the jar. There's installation instructions on the download page in the website.