A variety of system reports are available to different users in Elentra. Some reports can be accessed from other screens, but most reports are accessed via Admin > System Reports.
Not all reports will be visible to all users and learners have no access to system reports (learners can access some reports on themselves depending on how you use Assessment and Evaluation).
Please note there are some specific reporting options for Courses, Course Websites, and Assessment and Evaluation. Please see the relevant help section for additional information on those reports.