Many posts tell you to copy files from
to your home directory.
Well, unfortunately that does not work for non-Ubuntu stuff.
Can anybody show me how to add this
xterm -bg black -fg white -fn 10x20
to my XTerm icon?
The file you are searching for under /usr/share/applications is debian-xterm.desktop.
Anyway, you don't actually need to copy this to your home directory, unless you don't have (or you cannot gain) the rights in order to write to this file.
If you have the rights to write to that file, open a terminal (or hit Alt+F2) and give:
gksudo gedit /usr/share/applications/debian-xterm.desktop
Once gedit opens, head to the
Exec field and place, instead of
xterm, your entry:
xterm -bg black -fg white -fn 10x20. Save the file and you are done.
If you don't (or you cannot gain) write permissions there, copy that file to your home directory (~/.local/share/applications/), edit it there, and you are done!
Another possibility is to launch "Main Menu" from Dash, find the Terminal app and modify the command.