You should include a comma in the following instances:
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To set off an introductory phrase - Yes, use a comma after an introductory phrase or clause.
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To separate the words in a series - Yes, use commas to separate items in a list or series.
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To show possession - No, commas are not used to indicate possession. Instead, apostrophes are used.
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To separate day from year in dates - Yes, use a comma to separate the day from the year.
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To start a list - No, this is not a standard use for a comma. A colon is typically used to introduce a list.
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To set off text inside quotes - Yes, use commas to set off dialogue or quotes when they are part of a larger sentence.
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To separate a city and a state - Yes, use a comma to separate the city from the state.
In summary, use commas for the first, second, fourth, sixth, and seventh instances.