If you need a general introduction, and some basic rules about punctuation, you can go to:
http://s170032534.websitehome.co.uk/punctuation.html-- it's a bit wordy, but covers all the basic stuff. The BBC also has a guide-- http://www.bbc.co.uk/dna/h2g2/A597143, which does the same thing.
Another good 'all-round' guide is http://owl.english.purdue.edu/handouts/grammar/.
Commas
For specific resources on comma use, try to the following:
http://www.bbc.co.uk/skillswise/words/grammar/punctuation/commas/
This is the BBC 'skills' website-- it's quite interactive, and relatively straightforward to use.
http://www.ssdd.uce.ac.uk/learner/grammar/commas.htm
A bit 'wordy', but covers everything.
Punctuating Speech
http://www.hermit.org/Blakes7/Fanzines/punctuate.html
This one's got a few basic rules.
I'll post more sites if needed, but these should be enough to get you started!
