Apart from the explanation in the grammar section you can watch this video for an interesting overview:
As for the future in the past, check this link from the BBC or this one from englishpage. Interested in online exercises? Try this link from OUP, or this one from englishdailyworkout, or another interactive one from learnenglish.org.uk.
Remember you have a great site in http://www.bbc.co.uk/worldservice/learningenglish/ for all kinds of stuff.