Punctuation marks are symbols that indicate the structure and organization of written language, as well as intonation and pauses to be observed when reading aloud.
In written English, punctuation is vital to disambiguate the meaning of sentences. For example, "woman, without her man, is nothing" (emphasizing the importance of men) and "woman: without her, man is nothing" (emphasizing the importance of women) have greatly different meanings, as do "eats shoots and leaves" (to mean "consumes plant growths") and "eats, shoots and leaves" (to mean "eats firstly, fires a weapon secondly, and leaves the scene thirdly").
The rules of punctuation vary with language, location, register and time and are constantly evolving. Certain aspects of punctuation are stylistic and are thus the author's (or editor's) choice. Tachygraphic language forms, such as those used in online chat and text messages, may have wildly different rules. For English usage, see the articles on specific punctuation marks.
Read more about Punctuation: History, Conventional Styles of English Punctuation, Other Languages