Learn Italian: Il corno rosso ti protegge? Tu ci credi? - Does the red horn protect you? Do you believe in it?

Here, ci replaces a phrase starting with the preposition a (in this case, al corno rosso). The verb credere uses the preposition a when talking about believing in concepts or superstitions. Instead of repeating Tu credi al corno rosso? (Do you believe in the red horn?), we use ci to say "Do you believe in it?".

Wait, why do we use credere a (which turns into ci) instead of credere in for "believe in"?

Italian generally uses credere a for believing that something is real or true, like magic, ghosts, stories, or good luck charms (like the red horn). Credere in is mostly saved for deep religious faith (like believing in God) or having confidence in someone's abilities.

Why does ti come before the verb in ti protegge?

ti is an object pronoun meaning "you". In Italian, object pronouns almost always go directly before the conjugated verb. So while in English we say "protects you", Italian says ti protegge (literally, "you [it] protects").

If credi already means "you believe", why is Tu included at the start of the second sentence?