Simplify the following text for a Grade 9 native English-speaking person.
Original: A lesson may be either one section of a textbook ( which , apart from the printed page , can also include multimedia ) or , more frequently , a short period of time during which learners are taught about a particular subject or taught how to perform a particular activity .
Simplified: A lesson may be either one section of a textbook or a short period of time during which learners are taught about a subject or taught how to perform an activity .