The best guide to the Fortran Programming language is the document called
Fortran Resources by Ian Chivers and Jane Sleighthome.
You may download a copy from the
FortranPlus website (look for a link to the Fortran Resource File).
This file is updated periodically, so check back occasionally.
A great feature of this file is that it is hyperlinked, so that you do not
have to copy the URL of a site and then type it into your browser in order
to visit the site. You just click it and it will open in your browser.