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.
Miscellaneous Additional Information
Fortran Library has useful information, but
was last updated in 2016.
FLIBS by Arjen Markus.
is another good site for explaining Fortran coding and exhibiting good examples.
Stuart Norris
keeps lots of links to numerical methods, especially in Fortran.
He also has links to other collectors, such as John Burkhart and Alan Miller.