Learn French: Vous vous brossez les dents le matin. - You brush your teeth in the morning.

The first vous is the subject ("you"). The second vous is a reflexive pronoun showing that the action is done to the subject (like saying "you brush yourself"). In French, verbs for daily hygiene routines like washing and brushing are usually reflexive.

Why is it les dents (the teeth) instead of "vos dents" (your teeth)?

In French, when you use a reflexive verb like vous vous brossez, it's already obvious whose body part is involved. Because the second vous tells us you are doing the action to yourself, French just uses the word for "the" (les) rather than "your".

Where is the word for "in" in le matin (in the morning)?

French doesn't use a preposition like "in" for general parts of the day. To talk about a habit, you just use le (the) plus the time of day. So le matin naturally translates to "in the morning" or "every morning".

Is this sentence talking to one person or multiple people?

It could be either! Vous is used to address a group of people (plural "you"), but it is also the formal, polite way to speak to a single person. The words and the grammar are exactly the same in both cases.