Calibre for Kobo to Kobo book transfer

Hey guys,
This is my first post on reddit and I don’t even know if I’m doing this right but I’d really appreciate any tips and pointers on what I should learn in order to use calibre to transfer books between my kobo and my daughter kobo. (We have seperate accounts on kobo) and I don’t want to double dip buying multiple copies of books. I’ve heard I should use calibre but haven’t been able to find a tutorial that shows my issue. If anyone can point me in the right direction I’d be super grateful, thank you!