There are a few different reports you can run to find when a chosen attendance code was used. These pages are particularly useful when checking the attendance for your School Census.
For full details of the available attendance codes and which count as absences codes, please see this guidance: Attendance codes and how they count towards statutory attendance
You can report on students that have a specific attendance mark (for example Illness) from your Raw Attendance Marks page. You can see how to do this here: Reporting on Raw Attendance Marks
You can generate a session absences report on all absence attendance codes and the dates in which the student had these marks from your Absentees by Date page. You can see how to do this here: Finding the N codes or other absence codes