Desktop Clicker is an idle game that runs overlayed on your desktop. It shows up over everything, so you can do other things while you play.
You need to run the Jar file from the current releases. A Jar is a Java executable, so you will need to install java (detail below)
To run the jar, (crossplatform) you need to install OpenJDK 21
Once you install the version corrsponding to your platform, you should be able to run the Jar.