Punctuation is often difficult in one's own language - it is, therefore, doubly difficult in a language that is not your own. In the following pages you can get the rules and practice in key problems associated with the common types of punctuation in English.
"Punctuation marks are signals to your readers. In speaking, we can pause, stop, or change our tone of voice. In writing, we use punctuation to emphasize and clarify what we mean." http://owl.english.purdue.edu/handouts/grammar/g_overvw.html