This punctuation mark has the following uses:
 To separate the items in a list:
… tens of thousands of them: Christians, Hindus, Muslims, Sikhs.
 To place a section of a sentence in PARENTHESIS (as brackets do):
Bill the dog, happy as ever to be out and about, was sniffing everything in sight.
 To mark the divisions between the CLAUSES in a COMPLEX SENTENCE:
These weedkillers may, if used on new lawns, damage young seedling grasses before they are well established.
 To separate sections of a sentence to make it easier to read:
To make a hot compress, pour hot water into a bowl and then add the essential oil.
 To introduce and/or end a piece of direct speech:
‘No, sir,’ said Stephen, ‘and that is what is so curious’.
You do not need to use a comma between nouns that are in APPOSITION:
My wife Dorothy
Alison and her friend Beth were attracted to the same man at a party.
Commas should be used to surround a noun that is in PARENTHESIS:
Pete, his son, cleaned the garden aviary.
Use a comma when writing a number that is made up of four or more figures:
23,500 1,500 miles.
But not in dates:
1 May 2004 the 1970s.
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