Collections organize your posts into categories. Use a tag to create a sub-category within a collection.
Collections
Collections appear on the menu bar of the Member Hub. Each collection should clearly define the posts members can expect to see. You can customize whether the ALL tab is displayed, and which collection is used as the home page.
Tags
Tags are keywords that define the post content. A post can have more than one tag and a tag can belong to more than one collection. When members click a tag, they are taken to a page that shows all the posts that are tagged with the same keyword.
You can also use tags to create secondary navigation from the collections menu.