When using quotation marks to enclose a direct speech or a quote, the period always goes inside the quotation marks. This is a rule that applies to American English only. Other punctuation marks, such as question marks, exclamation points, or colons, may go inside or outside the quotation marks depending on the context.
For example:
- "I'm going to the store," she said.
- She said, "I'm going to the store."
