Dear Confi ;)
First of all, please be aware that you cannot import the course total. The gradebook handles the aggregation of grades, and you can edit this aggregation, or even override the course total manually, but you cannot import it using a CSV file.
Secondly, it is essential that the user (Tom Jones, ID 1 in this case) be enrolled in this course. He must appear in the gradebook prior to your attempt to import grades for him. So you if you haven't yet imported or created any users into your course, you must do that first, and make sure that the ID numbers match those in your CSV file.
Next, you are mapping your "ID number" field with useridnumber. This is used to identify which user you are importing grades for. Please note that any other user data in your CSV file will not be used (if you have a different email address in your CSV file, it will not change the email address of the user already recorded in your target course).
The last part is to map your CSV fields to the grade items. Having created the Participation item, it should now appear as a mappable field for grades or comments (see attached screenshot). You must select that field in the menu adjacent to the Participation field of your CSV file, as shown in the screenshot.
Then, if you have identified the correct user, the grade will be imported.
I hope this clears up the confusion