Modules are top level containers with Security and Access Control. Submodules, also called libraries, are containers within the Modules with Security and Access Controls, Custom Fields, Workflows and can contain Items with Metadata, Documents, Tickets, Tasks and Reviews.
For example, a user can create a Module called Human Resources and create Submodules/Libraries such as Employee Folders, Policies and Procedures, Benefits, etc. Each of the Submodules can have its own Security Settings (access controls), Custom Fields where “Employee Folders” Submodule will require Employee ID Number, Employment Start Date, Termination Date, Manager’s Name, Department, etc. while Policies and Procedure Submodule will only require Policy Enforcement Date.