USE OF FULL STOP
1.At the end of a declarative and interrogative sentence:
The man arrived. He sat down.
2. With abbreviations (in an abbreviation the last letter of the word and of the abbreviation are not the same):
etc. (et cetera)
M.P. (Member of Parliament).
USE OF EXCLAMATORY MARK
1. To indicate strong feelings or a raised voice in speech
"Good heavens!" he said, "Is that true?
"Help!"
2. Many interjections need an exclamation mark:
"Hi! What's new?"
"Oh! When are you going?"