Learn Italian: Non correte nel corridoio, sento un passo! - Do not run in the corridor, I hear a footstep!

For the singular you (tu), the negative imperative uses non + the infinitive, so you would say non correre. However, this sentence is addressed to multiple people (voi). For both voi (you all) and noi (we), you simply use the regular present tense verb with non in front: non correte.

Why does sento mean I hear here? Doesn't it usually mean I feel?

The verb sentire covers several physical senses. Depending on the context, it can mean to hear, to feel, to smell, or to taste. Since the speaker is talking about a footstep (un passo), hearing is the only translation that makes logical sense here.

Why is it nel corridoio and not in il corridoio?

In Italian, the preposition in (in) almost always merges with the definite article that follows it. Since corridoio uses the masculine singular article il, in + il combines to make the single word nel.

What does un passo mean in this context?

While it can mean a mountain pass or a passage, its most common meaning is a physical step or footstep. The speaker is telling them to stop running because they hear the sound of someone walking nearby.