Punctuation mistakes occur when the correct symbols are not used in writing, leading to confusion or misinterpretation. Common errors include missing commas, misplaced apostrophes, and incorrect use of quotation marks. These mistakes can change the meaning of a sentence, making it important to understand proper punctuation rules. For example, the sentence "Let's eat, Grandma!" suggests inviting Grandma to eat, while "Let's eat Grandma!" implies something quite different. Understanding punctuation helps clarify meaning and improves overall communication, making it essential for effective writing in both casual and formal contexts.