Learn Russian: Куда вы едете? - Where are you all driving to?

Едете comes from the verb ехать, which specifically means to go by vehicle (driving, taking a bus, riding a train, etc.). If you were asking people where they were walking to, you would use идёте (from идти).

Why does this sentence start with Куда instead of Где?

In Russian, the word for "where" changes depending on whether there is movement toward a destination. Куда means "where to" and is always used with verbs of motion like ехать. Где means "where at" and is used for location, like asking Где вы? (Where are you?).

Why is the verb spelled едете? Doesn't the dictionary form end in -хать?

The verb ехать is a bit irregular in the present tense. The root changes from ех- to ед-. Because вы takes the -ете ending, it becomes едете.

The translation says "you all driving". Can this also be used to ask just one person?

Yes! The pronoun вы is used for "you all" (plural), but it is also the polite, formal "you" for a single person. You would use this exact same sentence to politely ask a single taxi driver, an older person, or a stranger where they are going.