SPARC Europe provides a very short guide to Open Access, and how to achieve it, called An introduction to the new model for scholarly communication.
They note the benefits for authors: "Rather than their paper being seen by readers at the few hundred institutions lucky enough to have a subscription to the journal, the paper can now be seen by all interested readers. This increases the dissemination and impact of the papers and so raises the profile of the authors and their institutions."
The guide also highlights the 2 routes to Open Access: Self-archiving and Publishing in Open-access journals
A useful resource supported by SPARC Europe, is the (DOAJ).