Many writers have an idea of who their readers are. Some do, because they write genre fiction, so a thriller writer knows that they write for people who enjoy reading thrillers, a romance writer often thinks of their audience as women, a young adult writer sees their readers as young people, probably under 20.
As a teacher, you will also have imagined who your students/readers are.
Here in SenGuide, we are writing and teaching as older, experienced people for older people who may not have experience in the same areas as we do. But maybe you also want to pass on your knowledge to younger people. In any case, we will now imagine our readers/students.
A persona is a representation, an imagined person. To build our class of imagined students, we will need more than one persona, but probably not too many. Each will need to represent a group of people who could be interested in your class. We could say that our class will consist of 6 personas.
Create 6 personas, 6 people who will take your class. This is a little like writing characters for a novel. Take a page for each persona. Give them a name, and some distinctive characteristics.