Hi Helena
The help documents for multichoice multiple answers is here - if you have three correct answers you would award a Grade of 33% for each correct option as the mark for the question should add to 100% . The wrong answers would be given a grade of 0.
For deleting a course see the help here - selecting the x from the course and category management should do this. Ensure that there is no one enrolled on the course that you wish to keep records for.
There are also free courses on the Totara Academy and if doesn't help then creating a ticket in the helpdesk will get more specific support.
Regards