When your database is set to track attendance you will find the Attendance Report under the Reports menu, in the Students section. This report compiles a list of student attendance during the time frame used for the report.
Several filters are available to select which classes you want to look at.
Class Attendance in the Staff Portal
The same situation is also used in the Absences/Makeups Report Help article to contrast the difference between tracking attendance vs tracking absences.
In this class, there are four students enrolled in the Ballet - Beg - F class. When attendance was taken in the Staff Portal there were three students present and one student absent.
The Attendance Report for 2/14/2020 displays the 3 students who attended that day:
The Attendance tab on the Class record shows 3 of the 4 students as having attended on 2/14/2020: