It depends how you want to offer the course. With InDesign you can produce digital publications in formats such as PDF, ePub (FXL and Reflowable text) Publish Online and Apple iBooks. If you want a website, then Muse or Dreamweaver are the tools to use. Adobe Captivate is described to be for eLearning. Nowadays, such courses use a mix of these and it's known as "blended learning".
None of these applications would be described as easy to learn. Lynda.com have online video training courses on all them.