used to express negation or absence

नहीं

English Usage: There was no milk left in the fridge.

Hindi Usage: फ्रिज में दूध नहीं बचा था।

at the present time

अब

English Usage: Now is the time to act.

Hindi Usage: अब कार्य करने का समय है।

used to give a negative response

नहीं

English Usage: "Do you want to go?" "No, I’d rather stay home."

Hindi Usage: "क्या तुम जाना चाहते हो?" "नहीं, मैं घर पर रहना चाहूंगा।"

not any

कोई नहीं

English Usage: There were no options left for us.

Hindi Usage: हमारे लिए कोई विकल्प नहीं बचा था।