Mark a class present or absent for the day — absent parents are alerted by SMS.
Go to Attendance and pick the year, grade, section, and date. The date defaults to today.

Class teachers only see their own sections in the pickers; admins see every class.
Tap a name to mark that student absent. For a routine day, use 'All present' and then flag the few who are out.
Press Save. An SMS goes to the parents of absent students (once SMS is switched on for your school).
To edit a past day, a class teacher submits a correction request that an admin approves under Attendance → Corrections. Admins can edit past days directly.