(Often with that: now that)
Définitions
Used to introduce a statement that contrasts with or seems to contradict something that has been said previously. She said she would help, now she refuses to even talk about it.
Used to introduce a new topic or to resume a subject after a pause. Now, let's move on to the next item on the agenda.
Used to draw attention to a particular statement or point in a conversation. Now, let's discuss the main issue at hand.