It means "Do you speak French?" and would be used with an authority, stranger, or more than one person.
If you were talking to 1 pet, 1 little kid, or 1 friend/someone you know very well you would say: "parles-tu francais?" (pronounced "parl too fransay?") which means exactly the same thing but has the informal word "tu" meaning "you" instead of the formal/plural "vous" meaning "you".
Comprenez-vous??? ("do you understand?")
Comprends-tu??? ("do you understand" - informal!!)
parlez vous francais means do you speak french?
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