— Per guidelines for American English, not British English.
Essentially, quotation marks "embrace" an individual's spoken words.
1. With attribution (commonly known as a dialogue tag), a direct quote should be surrounded by quotation marks.
Incorrect:
I must marry the most interesting man in the world said Betty Lou.
Correct:
"I must marry the most interesting man in the world," said Betty Lou.
— The use of a comma after the final word of the quote and BEFORE the closing quotation mark indicates the reader should pause and recognize Betty Lou is the speaker.
2. Quotation marks should also surround a direct quote indicating what one party says another party said.
Incorrect:
Betty Lou says she wants to marry the most interesting man in the world said Ralph.
Correct:
"Betty Lou says she wants to marry the most interesting man in the world," said Ralph.
— Ralph is speaking about what Betty Lou said. His comment is considered the quote (even though he's talking about what Betty Lou said) and must have quotation marks to indicate such. The use of a comma after the final word of his quote and BEFORE the closing quotation mark indicates the reader should pause and recognize Ralph is the speaker.
3. If the first portion of a quote includes a dialogue tag, the completion of the thought does not require additional attribution.
Correct:
"Betty Lou says she wants to marry the most interesting man in the world," said Ralph. "She'll never agree to marry me."
— The first portion of the quote is attributed to Ralph. The quote directly after, also Ralph's, does not require additional attribution. It is part of the same paragraph and completes Ralph's thought about his marriage prospects.
4. If a speaker asks a question or exclaims dramatically, replace the comma with the appropriate punctuation (after the final word of the quote and before the closing quotation mark).
Correct:
"Betty Lou says she wants to marry the most interesting man in the world?" asked Ralph. "I'm doomed."
Correct:
"Betty Lou says she wants to marry the most interesting man in the world!" exclaimed Ralph. "I'm doomed!"
5. Attributing dialogue tags may be placed at the beginning or end of a quote ... or even in the middle.
Correct:
Ralph said, "Betty Lou says she wants to marry the most interesting man in the world."
Correct:
"Betty Lou says she wants to marry the most interesting man in the world," said Ralph.
Correct:
"Betty Lou says she wants to marry the most interesting man in the world," said Ralph, "and that I don't even come close."
— No matter where an attributing dialogue tag is placed, it should be separated from the quote with proper punctuation, so the reader knows to pause and recognize the speaker. Note: In the case of placing attribution before the quote, the comma should appear just after the attribution and BEFORE the opening quotation mark. In the case of placing attribution after the quote, the comma should appear after the final word of the quote and BEFORE the closing quotation mark. In the case of placing attribution in the middle of a quote, the comma should appear just after the attribution and BEFORE the second quoted phrase (which is not capitalized unless it starts with a proper noun). It may be helpful to read the quote aloud, to determine where best to place the attribution.
6. A paraphrased statement may stand alone without quotation marks.
Correct:
Betty Lou insists she wants to marry the most interesting man in the world.
— This sentence does not give attribution to the speaker and is a general statement of what is happening, not an actual sentence spoken by Betty Lou.
7. A partial quote may be set apart with quotation marks.
Correct:
Betty Lou insists she wants to marry "the most interesting man in the world."
— The quoted words spoken by Betty Lou are part of a longer paraphrased, general statement. The quotation marks serve to indicate the exact partial quote spoken by Betty Lou.
8. A partial quote used in a full quote may be set apart with single quotation marks, if it is necessary to highlight its importance.
"Betty Lou insists she wants to marry 'the most interesting man in the world'," said Ralph.
— In this case, the comma falls between the closing single quotation mark and the closing double quotation mark.
There are many nuances to structuring dialogue. The above suggestions barely scratch the surface of letting voices speak on the page. For more info, visit one of my favorite grammar blogs at www.grammarly.com.
Happy writing.
P.S.
When it comes to marriage, Betty Lou says, "Ralph really needs to step up his game with the ladies."