Being a computer literate senior, I would suggest a few things, some of which are general.
- Divide your class (if there are enough people) by computer literacy
- Be sure to explain Digital Rights Management (DRM) so they are aware of the restrictions & limitations that DRM causes
- Point out that there are places where they can get DRM-free ebooks, e.g. here at MobileRead, Baen.com
- And last but very important, point them to this site.
And another thing, be sure to point that most ebook reading software allows you to increase the font size. This is an important feature for seniors.