Backup defaults doesn't have a path.
Automated backups do:
Then, if I set manual, do I have to specify the days of the week? it seems strange that it is allowed to select
If set to manual it means you, which I doubt, will run the autobackup script in admin/cli/.
the folder where I want the backups of the courses to be saved resides
in the same position as the moodle and moodledata folders, how can I
indicate this folder? writing "/ coursebackups"?
Now we are into basic understanding of shared hosting and the slice of space you have on such systems as well as Linux .... if you do /coursebackups ... the slash in your case is at the root of shaered server - uhhh, you don't have access to that area I would hope.
One has to use full paths. Since you insist on nothing but GUI (cPanel), learn your system. Your hosting provider should have tutorials/docs for customers. Your assignment ... find out about full paths in your account on the shared system provided by provider.
Will give one caution about autobackups ... don't select 'keep all' in the setup. Why? You don't have unlimited space and will probably forget all about checking autobackups and space. Run out of space and that will affect users ability to even login.
'spirit of sharing', Ken