Exclamation marks.
These are placed at the end of words that are cried out loudly.
The words before maybe a single word, such has a command, or a phrase or sentence.
A verb can stand alone as an exclamation, making a complete sentence. (Stop!)
An exclamation mark acts as a full stop when it is at the end of a sentence so you don't need a full stop as well.
Remember to use a capital at the beginning of a sentence FOLLOWING an exclamation mark.
example: Clang! The ancient bell on the front door rang. She rushed into the hall,exclaiming, 'Oh my goodness!'
One last thing do not over use them as it make the writing a jerky and rather irritating appearance and style.
Never use more than one at the end of a sentence unless its informal or to a friend.
Thank you.