It took me a whole hour to figure how to set up a .desktop file on Ubuntu which honestly seems unnecessarily complicated. In previous versions of Ubuntu, there was a GUI (gnome-desktop-item-edit) which aided in this process but unfortunately, this appears to have been removed. Here are some useful notes to set up .desktop files

• .desktop file format example

#!/usr/bin/env xdg-open

[Desktop Entry]
Version=1.0
Type=Application
Terminal=false
Exec=/usr/bin/gedit %U
Name=Test_1
Comment=comment here
Icon=

• What's the %U in the Exec file?

It's a parameter for the Exec key in .desktop files (defined in the Desktop Entry Specification) that describes how arguments to the program (from the file manager/program launcher, e.g. multiple selected files) should be handled

• Make the desktop file executable and copy it to /.local/share/applications
• Launching the file from the terminal

gtk-launch something.desktop