Bookshare is an online accessible digital library for individuals with print disabilities. In 2007, Bookshare received a grant from the US Government's Office of Special Education for make the service available for free to all students with a documented print disability in the US. Eligibility requirements are listed on the here on the website.
Bookshare is not a very difficult service to use, but like using anything else, it helps to have some guidance. The National Center on Accessible Instructional Materials has straightforward video tutorials on how to use Bookshare.
These videos can be used as instructional material on how to teach someone to use Bookshare or as a reference for students and families.