Learn French: Continuez tout droit, le parc est à gauche. - Continue straight ahead, the park is on the left.

This sentence uses the imperative mood to give a direction. Just like in English, when you give a command in French, you drop the subject pronoun. So, instead of Vous continuez (You continue), you just say Continuez (Continue).

How would I say this to a friend or someone I use tu with?

You would use the tu command form. For regular -er verbs like continuer, the imperative is made by taking the present tense tu form (tu continues) and dropping both the pronoun and the final s. So, you would say: Continue tout droit...

Doesn't droit mean "right"? Why does the translation say "straight ahead"?

This is a very common mix-up! While à droite means "to the right", the exact phrase tout droit is a fixed expression that means "straight ahead". Pay attention to the spelling and the word tout before it to tell them apart.

Why do we use à in à gauche instead of the French word for "on"?

In English, we say "on the left", but French uses the preposition à (which usually means "to" or "at") for these directions. You will always see à gauche for "on the left" and à droite for "on the right".