A good way to learn about grammar use is to read a high-quality, free online grammar guide. Two popular guides are Grammar Girl, located at QuickandDirtyTips.com, and the Purdue OWL, located at OWL.English.Purdue.edu.
The Purdue OWL, short for Online Writing Lab, is a collection of writing resources maintained by Purdue University. Its general writing resources include extensive advice on commas, apostrophes, hyphens and quotation marks. It also offers handouts that examine common punctuation patterns and how to punctuate different types of clauses, as well as exercises for practicing these skills. The exercises are printable, and the answers to all questions are available on the website.
The Purdue OWL also offers limited individualized help that is not limited to students of Purdue University. Its website includes a form with space for questions or very small writing samples. Purdue graduate students look at incoming forms and respond with appropriate writing advice.
Grammar Girl is the website of award-winning writer and Stanford graduate Mignon Fogarty. Her website includes articles on correct punctuation use, such as "How to Use Quotation Marks," "How to Use Commas: A Summary," and "Exclamation Points." Other articles, like "Numbers in Parentheses," examine more specialized topics for more advanced students.