Jane first meets Mr. Rochester as she walking in the dusk on a cold January day to mail a letter in Hay for Mrs. Fairfax. She sees a large dog, hears the thunder of a horse going by, and then hears Mr. Rochester fall from his horse. She has no idea who he is, but she goes to help him. She is not afraid of him, not knowing he is her employer, and allows him to lean on her as he limps forward on a twisted ankle to remount his horse.
He asks her questions but doesn't reveal his identity. It is only after she is back at Thornfield that Jane learns it is her employer she has helped.
The first meeting is important because it occurs in a romantic, liminal space in nature as dusk is changing into nightfall, presaging the gothic qualities of their romance. It also foreshadows the way Rochester will withhold information and keep secrets from Jane and how they will become equals at the end of the novel due to injuries that make him dependent on her.