Well, the 'normal' way to create a Moodle question is:
- Go into any Course where you have teacher editing rights.
- Go to 'Question bank' in the course settings menu.
- Click 'Create question ...'.
- Select 'Numerical' and click Continue (or whatever the button is called).
- Fill in the form and save.
The method of creating questions by importing a file is less common (but sometimes extremely useful).
The easiest way to work out the XML format is to make a question in Moodle, then export it.
If you don't have any other Moodle site available, you can use demo.moodle.net, providing you watch out of the one-hour reset there. Or sign-up for a free MoodleCloud site.