Enclose the field in quotes, e.g.

field1_value,field2_value,"field 3,value",field4, etc...

See wikipedia.

Updated:

To encode a quote, use ", one double quote symbol in a field will be encoded as "", and the whole field will become """". So if you see the following in e.g. Excel:

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| regular_value |,,,"|  ,"", |"""   |"|
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the CSV file will contain:

regular_value,",,,""",","""",","""""""",""""

A comma is simply encapsulated using quotes, so , becomes ",".

A comma and quote needs to be encapsulated and quoted, so "," becomes """,""".