To ask questions, you have to use a special question word ar:

Ar yra Vytautas? Is there Vytautas?
Ar jis kalba? Does he speak?
Ar jo sesė eina? Is his sister going?
Ar jos sesė eina? Is her sister going?
Ar mes čia esame? Are we here?
Dariau, ar tu kalbi? Darius, are you talking?
Ar jūs kalbate lietuviškai? Do you speak Lithuanian?
Ar tavo vardas Darius? Is your name Darius?

However, it is not always necessary to use ar. If you raise your intonation in the end, you can omit ar:

Jis kalba? Is he speaking?
Dariau, tu kalbi? Darius, are you speaking? Darius, you speak?
Jūs kalbate lietuviškai? You speak Lithuanian?