Next to completely hiding content in a class, it's also possible to lock content in a class. That way the students in the class see the content in their course structure, but they are not yet able to click it: it's grayed out.
Only after you as a teacher unlocked the content, they are able to click it.
Locking content is a way to be more explicit and in control over what content students can access, but still giving them the bigger picture of what is coming up later in the course. (In contrary to hiding content: then students do not see that content in the course structure)
Locking content can be done by clicking on the three dots next to the content you want to lock and select "Lock" in the menu.
The same functionality can also be accessed from the teacher menu. Go to "TEACHER" and then select "Chapters". In there use the right mouse button to open the menu: