On most Mondays of every week, you have the option to Instruct your students manually or automatically. Students gain skill experience quickly through Instructions. Leveling up their skill experience is required to unlock new classes and for them to learn new Abilities, spells, or Combat Arts.
The number of students you can manually instruct will depend on your Lesson Activity Points. (This can be seen in the Notes tab of Byleth’s profile) You can increase these points as your professor level increases.
During your lecture day, your students may approach you with their individual questions. Pick the correct answer (with their personalities in mind) to gain +50 motivation.
After the timeskip event, you can still teach your students in the form of training during your weekly war council. The mechanics of the study sessions you gave when they're still students will remain the same. Only the setting and some minor terms are changed.