How do I install this Ad-on??

[Erwin Ferguson]

I have entered the correct license, and downloaded the .jar file onto my JIRA server. The .jar installation file will not execute when I click it, and the ad-on does not appear anywhere on the top bar of JIRA where the Projects, Issues, and Dashboard drop-down menus are located. Please help!

[Nic Brough]

Ideally, you should use the UPM to install new add-ons, not an upload.  I don't know why you're expecting a click to execute it - add-ons run inside JIRA, not standalone.   For an upload, you should be using "upload" from the manage add-ons page, and there's nothing to click and run there either.  .jar files can be "run" if they're a standalone, but Atlassian add-ons are not standalone items.

Also, we don't know what add-on it is.

Could you try again, but use the recommended route - via "find new add-ons"