"¿Tú tienes una hermana?"
Translation:Do you have a sister?
Do Tengo and tienes mean the same i.e. have? If yes, when to use which word?
They're both parts of the conjugation of tener (to have):
(Yo) tengo = I have
(Tú) tienes = you (familiar) have
(Él, ella, usted) tiene = he, she has; you (formal) have
(Nosotros/as) tenemos = we have
(Ellos/as, ustedes) tienen = they, you (plural) have
As you can see, most of these mean have, but the one you use depends on the subject of the sentence. Since the subject of Duo's sentence is "Tú," you use the tú form: tienes.
"I have" a sister. = "Yo tengo" una hermana.
"You have" a sister. = "Tú tienes" una hermana.
"Tengo" is "I have" and "Tienes" is "you have"