Hi John Francis, I recommend looking at "http://simple.wikipedia.org/wiki/Punctuation" for punctuation rules in general. Kind regards from Georg (in Austria)

One possible reason for the struggle is that punctuation is used differently in different languages. I'm forever re-schooling my students on using commas simply because English and Slavic languages use commas differently. Try posting your writing in Notebook and get some corrections. Feel free to ask why the member corrected your sentences (they should give you a clear reason). http://www.italki.com/notebook

A comma is used when you pause, like when you are speaking, you pause to breathe, then you continue. A full stop comes at the end of the sentence, when you have finished that thought or phrase.