Hello Denis,
Please check the business configuration activity : Set of books which is can be accessed by following the below steps.
1 - Business configuration work center
2 - Implementation project view
3 - Select the project and click on Open activity list
4 - Navigate to Integrate and extend tab
5 - Search for activity - Set of books
Also refer to help center document :
1) Set of books
2) Reporting Principle
Regards,
Harshal Vakil