When we write speech we need to remember to add other punctuation as well as the speech marks (the 'sixty sixes' and 'ninety nines').
"I'm tired," sighed Joe.
In this sentence there is a comma after the word 'tired' but before the closing speech marks.
Sometimes we need to use a question mark or an exclamation mark instead of a comma.
"What time is it?" asked Kim.
"Listen to me!" shouted Paul.
If we begin the sentence by saying who is speaking, we put a comma after their names but still begin the speech with a capital letter even though it is not the beginning of the sentence.
Joe sighed, "I'm tired."
Kim asked, "What time is it?"
Paul shouted, "Listen to me!"
If you look carefully at what Joe says you will see that there is a full stop this time instead of a comma after the word 'tired'. We never finish a sentence with a comma.