Definition of "Now" :

noun: the momentary present

"Now is a good time to do it."

adverb: in these times

"It is solely by their language that the upper classes nowadays are distinguished."

adverb: without delay or hesitation; with no time intervening

"Come here now!."

adverb: used to preface a command or reproof or request

"Now hear this!."

adverb: at the present moment

"Goods now on sale."

adverb: in the historical present; at this point in the narration of a series of past events

"President Kennedy now calls in the National Guard."

adverb: in the immediate past

"Told me just now."

adverb: (prefatory or transitional) indicates a change of subject or activity

"Now the next problem is...."