The Modules tool serves to organize different types of course content into a sequence for users to follow. Modules are often organized chronologically (by week) or topically. Teachers have the option to require students to mark one module item read before accessing the next or to set prerequisites or date restrictions. So, students can move through material at a pace you determine in your module settings.
Each module has its own published status separate from its contents. If a module is unpublished or date restricted, then its contents (files, pages, assignments, etc.) will be inaccessible to students, even if they are published individually. That is, the module's unpublished status overrides the content's published status. To fix the issue where students cannot access content included in an unpublished module, either (a) remove the content from the module to make it accessible elsewhere, (b) move the content to a published, non-restricted module, or (c) publish the module.
Reminder: Modules cannot contain modules (i.e. module within a module).
Instructure Guides: