A comma is inserted after the name of a person or thing addressed.
“John, you were mistaken.”
“My country, I am proud of thee.”
Period.—The period (.) is put at the end of every complete sentence that is not exclamatory or interrogative. It is also used as a part of every abbreviation, and after every initial letter standing in place of the full word in a name. “A. M.” (for Master of Arts), “Mr.” (for Mister), “Esq.” (for Esquire), “R. W. Emerson” (for Ralph Waldo Emerson), “Dr.” (for doctor).
Note of Interrogation.—The note of interrogation (?) should follow every direct question: “Are you coming?” “Shall I buy it?” An interrogation point does not, however, follow an indirect question, such as “Let me know what he says.”
Note of Exclamation.—The note of exclamation (!) follows an exclamation, or any series of words denoting an outburst of feeling. “Alas!” “Three cheers!” “Hurrah!”
Colon.—The colon (:) is used to divide from one another the several co-ordinate members of a compound sentence, when they might each of them form an independent sentence, but are ranged side by side in a compound sentence for the sake of better showing how they illustrate one another.
“New York is a wonderful city: The wealthiest in America.”
A quotation or enumeration of details is often preceded by a colon.
“He spoke as follows:” “His last words were:” “Among those present were:”