Learn Italian: Ci rispondi sempre. - You always answer us.

In English we say 'you answer us,' but in Italian the verb rispondere (to answer) works like 'to answer to someone.' Because of this, ci acts as an indirect object pronoun here, literally meaning 'to us.'

Why does ci come before the verb instead of after it?

In Italian, these short object pronouns (called clitics) almost always go right before the conjugated verb. So instead of following the English order 'answer us,' the Italian word order is literally 'to us (you) answer.'

How do we know it means 'You always answer' when there is no word for 'you' in the sentence?

The ending of the verb gives it away! The verb rispondi ends in -i, which is the regular ending for tu (you, singular) in the present tense. You do not need to include the word tu because the verb already shows who is doing the action.

Could I put sempre before the verb, like 'Ci sempre rispondi'?

No, that would sound unnatural. In English we often put 'always' before the verb ('You always answer'), but in Italian, adverbs of frequency like sempre usually go immediately after the verb they describe.