as = cuando, mientras
As I came in, I saw that the house was full of guests.
Cuando entré, vi que la casa estaba llena de huéspedes.
Mary made some fresh coffee, as we were talking about the future.
Mary hizo un café, mientras nosotros hablamos del futuro.
As they were walking down the street they met a lot of people.
Bajando la calle, veían mucha gente.