Lay out each class's weekly periods, and cover absent teachers with substitutions.
Go to Timetable and pick the class. Add each period with its day, time, subject, and teacher.

Add periods across the week. If a teacher is double-booked at the same time in another class, Campustics flags the clash as you go.
When a teacher is out, open Timetable → Substitutions, pick the absent teacher and day, and Campustics ranks free teachers for each of their periods.
Substitution suggestions put subject-matched, already-on-campus teachers first.