Use an exclamation point to show surprise or strong emotion.

In those few moments of geologic time will be the story of all that has happened since we became a nation. And what a story it will be!

– James Rettie, “But a Watch in the Night”

Use exclamation points very sparingly because they can distract your readers or suggest that you are exaggerating.

Do not use a comma or a period immediately after an exclamation point that ends a direct quotation.