A course is a bundled sequence of training. A course might be comprised of 1 or 2 videos to watch, a listening guide to download and use, and a website to visit to find additional resources.
A workflow is a combination & sequence of courses that are assigned to users. A workflow supports the scope & sequence of training and allows training to better build on top of either other.
Additionally, with workflows, you can add email communication throughout a workflow to communicate to your participants before and after they complete specific courses.