Punctuation marks are symbols used in writing to separate sentences and clarify meaning. The main punctuation marks are the period, comma, brackets, exclamation mark, semicolon, colon, apostrophe, question mark, and hyphen. Each mark has a specific grammatical purpose, such as commas separating items in a list, periods ending statements, and question marks ending questions. Punctuation is important as it can change the meaning of a sentence depending on where marks are placed.