When following guides, it is often asked to edit files, most often in template but sometimes in qubes themselves.
This is a guide that explain on a template by template basis, how to edit a file. The audience are beginners who do not know how to edit files from a terminal or very little experience with Linux.
Now you can start the editor in that qube from the Qubes OS menu. In the Text Editor program, click on the top left button "Open", then click on the "Icon" in the small popup and browse the file system to find the file you want to edit. If you need to create a new file, write the content then save to the location you want.
Note that if you edit a file that should be edited as root (the admin user), Text Editor will automatically escalate privileges to have the permissions to edit the file, this is possible without password because qubes do not have a root password by default.
You can start the program from the terminal using gnome-text-editor and you can add a parameter to it for a file location if you want. This does not work if you add sudo to this command.
Now you can start the editor in that qube from the Qubes OS menu. In the program Mousepad, click on the menu "File", then click on "Open" browse the file system to find the file you want to edit. If you need to create a new file, write the content then save to the location you want.
Note that if you edit a file that should be edited as root (the admin user), you need to start Mousepad from the terminal to run it as root:
type sudo mousepad
you can close the terminal once you finished with Mousepad