You can define substitution specific information for each teacher in menu Settings/Teachers:
A: First column specifies if the teacher can do substitutions at all.
B: In the second column you can set duty and time-off for teachers. After click on small timetable icon this window will appear:
Grey fields represent actual timetable of this teacher and with multiple click you can set:
Red "X" - teacher cannot do substitution at certain period,
Duty - if some teacher is not available, this teacher has to be ready to be called.
Overtime - in some countries they define certain lessons as overtime. The software then reports how many overtime lessons the teacher did.
C: In the third column you can assing teacher to the approbations (groups of teacher, who can proffesionally substitute).