The discussion of report definition is found in the lesson "Building Business Reports" in SAE II. You may want to enrol in the course to learn more about this.

There is also a dedicated PRPC Topic on Reporting that can be found here: https://pdn.pega.com/browse/prpc-topics/reporting

Here is also an article on creating a report definition. The screenshots are taken in PRPC 6.x but the concept is applicable in Pega 7.1.7: https://pdn.pega.com/reporting/report-definition-rules-beyond-the-basics

In a section rule, you can add a Repeating Layout. The repeating layout can source a Report Definition.