Punctuating dialogue can be more difficult than punctuating regular sentences, because it's not always clear when the sentence is over. After a character says something, is the sentence over? Or is the sentence over after you've told the reader which character spoke? The answer is, both. It depends on what the character is saying. If your character is saying something simple (ie: one sentence) then you use a comma at the end, right before the quotation mark, and end the entire sentence in a period: "What a cute dog," said Sally. "But," pondered Sally, "is the dog for sale?"