The Spanish verb faltar literally means "to lack" and it is a cousin of the English word "fault," which in Middle English often described a "failing" or "lack". The word faltar has many uses, and "to lack" isn't always the best translation. Faltar often indicates that something or someone needs something. The person or thing in need is often referred to using an indirect-object pronoun, while what is needed or lacking (a direct object) can be a noun, like arete (earring), or sal (salt).
(A tu novia) le falta un arete.
She (your girlfriend) is missing an earring.
(A la sopa) le falta sal.
It (the soup) needs salt.
What's lacking can also be a verb in infinitive form, like dormir (to sleep).
A José y Pepita les falta dormir más.
José and Pepita need to sleep more.
Finally, faltar is not an impersonal verb, but it's very common to use it impersonally (always in the present tense):
Antes de eso falta servir la cena.
Before that, dinner needs to be served.
Falta mucha ingenuidad para ser engañado por alguien como tú.
One needs to be very naive to be fooled by someone like you.
And now, to hear how Candelario uses faltar in context, click on the following free demo of the Yabla Player. Thanks for reading!
Abuelo, pero todavía nos falta hacer la película. -¡Sí!
Grandfather, but we still have to make the movie. -Yes!Play Caption