Active collections are those collections published and visible to your viewers. Depending on your account type, you may have more or fewer active collections. Limits are indicated on your Manage Collection page, and there is a limit on the number of active collections you can have.
A default collection is what your users will see when they come to your page without specifying any collection.
For example, if your page is "josmistreamloots", then that's the collection that your users will see when they arrive at streamloots.com/josmistreamloots.
Changing your default collection
To change the default collection, drag and drop the collection you want to mark as default to the top of your collections list. The collection at the top will be your default collection.