There are three types of communities: generic communities, learning module communities and course website communities.
A community (most generic) would be most appropriate for a school committee, student work group, or social group. By default it just has a home page but users can add announcements, discussions, document sharing, etc. Through these functions you can post announcements (and send email notification of announcements to registered community members), host discussions, use poll and quiz functions, etc. Examples: Curriculum Committee, Surgery PBL Group 2, Undergraduate Cooking Club.
Learning module communities are most appropriate to use if you want to create an educational module for users (e.g. a module on infection control in the hospital). The pages you can select from include introduction, objectives, foundational knowledge, testing understanding, etc. Users will be able to navigate through the pages as you've set them up. You can embed video, images, etc.
You can use a course website community to turn the basic information about a course completed through the course set up page, into a course website. A course website uses a template to create pages like background, course calendar, units, prerequisites, course aims, etc. The Learning Objectives and MCC Presentation pages are configured to auto-populate with the curriculum tags assigned to the course through the course setup.