Okay; this is the sort of thing that gives grammarians a bad name. But if you want to be an effective writer, it's the sort of thing you should take an interest in.
4 Punctuation Marks for Forming Appositive Phrases
http://www.dailywritingtips.com/4-punctuation-marks-for-forming-appositive-phrases/
4 Punctuation Marks for Forming Appositive Phrases
http://www.dailywritingtips.com/4-punctuation-marks-for-forming-appositive-phrases/
