You can decide what items in the course menu that are visible/hidden for students (the crossed eye indicates that the item is hidden for students). Every course has it's own settings but the current default active links are: Announcements, People, Modules and Grades. But this can be changed.

Click Settings in the course menu to open the view.
Click the Navigation tab.

course menu

Drag and drop items and reorder them the way you want. All the items above the middle of the page are visible. The ones below stay hidden. When you are done click the Save button.

course menu gif

When the crossed eye is removed in the course menu, the item is visible for students. The only exception is Settings which is for teachers only, regardless of the missing crossed eye.

Note!

If an item is activated but contains no content, the eye will still appear and the link will not be visible for the students until you add some content. For example, Announcements has a crossed eye until you post your first announcement. This is intended behavior and not a support case.