Read the dictionary definition of now. All definitions for this word.
1. the momentary present
1. Now is a good time to do it
2. it worked up to right now
2. in these times
1. it is solely by their language that the upper classes nowadays are distinguished
2. we now rarely see horse-drawn vehicles on city streets
3. today almost every home has television
3. without delay or hesitation; with no time intervening
1. he answered immediately
2. found an answer straightaway
3. an official accused of dishonesty should be suspended forthwith
4. Come here now!
4. used to preface a command or reproof or request
1. now hear this!
2. now pay attention
5. at the present moment
1. goods now on sale
2. the now-aging dictator
3. they are now abroad
4. he is busy at present writing a new novel
5. it could happen any time now
6. in the historical present; at this point in the narration of a series of past events
1. President Kennedy now calls in the National Guard
2. Washington now decides to cross the Delaware
3. the ship is now listing to port
7. in the immediate past
1. told me just now
8. (prefatory or transitional) indicates a change of subject or activity
1. Now the next problem is...
See also: Merriam-Webster definition of now