I opened the app, but nothing happened.

Once you open the app, you can access it by going to the menu bar at the top right of your screen. Look for the app icon.  If you don't see it there, you may have too many apps in your menu bar.  Try closing some of the other apps in the menu bar.  Alternatively, you can manage which apps have priority in your menu bar by using an app such as Bartender:
https://www.macbartender.com