You might have installed an application by downloading a zip file and unzipping it. Maybe into the /opt/ directory. How can you run it from the GUI of Ubuntu?

For example when I downloaded Postman I unzipped it to be in /opt/Postman.

I could run it from the terminal by typing in /opt/Postman/Postman but I wanted to run it from the Desktop GUI of Ubuntu.

So I created a file called ~/.local/share/applications/postman.desktop with the following content:

examples/postman.desktop

[Desktop Entry]
Terminal=false
Type=Application
Name=Postman
Exec=/opt/Postman/app/Postman
Icon=/opt/Postman/app/resources/app/assets/icon.png
#NoDisplay=true

Then ran 

chmod 664 ~/.local/share/applications/postman.desktop

It was not that simple, I fought with this a bit, I even logged out and in a few times as that was suggestied on some place, but I think that was not necesseary I just had to get the fields in the file right.

Now I can press the "Windows key" on my keyboard, start typing "post..." and I can launch the app.

When it is running I could go to the menu on the left-hand side, right-click on the Postman icon and click on Add to Favorietes so it will stay in that menu even when I quit the application.