Credo material can easily integrate into the Grades section of your D2L instance. If you do not need it to integrate with your gradebook, or if there are no quizzes, a simple web link may be best. You can, however, still use the following method to add a .zip file as a module but not add a link to your grades. That decision is up to you. For specific examples of how to import a .zip file so it integrates with your gradebook, see the tutorial below.
PLEASE NOTE: If you or a faculty member ever want to delete a module, you MUST disassociate it from any gradebook items first, otherwise it may never let you delete the gradebook item since it thinks it is still associated with something. So the important thing with D2L is to "disassociate before deleting".