Learn French: Bonjour, Monsieur, vous êtes français ?

Vous is usually the plural "you", but in French, it is also used as a formal "you" for a single person. Because we are addressing a Monsieur (sir) to show politeness or respect, we use vous instead of the informal tu.

If vous takes a plural verb, why doesn't the adjective change to match a plural?

Even though the pronoun vous takes the plural verb êtes, any adjectives still match the actual person you are talking to. Since this formal vous refers to one single man (Monsieur), the adjective français remains singular and masculine.

Why is français written with a lowercase "f"? In English, we capitalize "French".

In French, nationalities are not capitalized when they are used as adjectives to describe someone or something. They are only capitalized when used as a noun to name a person, like un Français (a Frenchman).

How do we know this is a question if the words are in the same order as a regular statement?

In everyday spoken French, it is very common to ask a question simply by keeping the normal sentence order (vous êtes français) and raising your voice at the end, just like saying "You are French?" in English. You don't always need special question words or to flip the verb around.