Not: không before the verb or adjective

Không before a verb or an adjective means "not": Tôi không uống cà phê. I don't drink coffee. Hôm nay trời không nóng. It isn't hot today. Nothing else changes: there's no extra word like "do" or "does", and the verb stays the same for every person.

The past works the same way: Hôm qua em không đi làm. I didn't go to work yesterday. The time word shows it's past, so you usually leave out đã. With sẽ (will), không comes after it: Tôi sẽ không quên. I won't forget.

On its own, Không means "no", the answer to a có … không question. In the South a polite "no" starts with dạ: Dạ, không.

In everyday sentences, không doesn't go straight before là. For "is not" with a noun, say không phải là: Tôi không phải là người Mỹ. For "not yet", use chưa: Em chưa ăn means "I haven't eaten yet", while Em không ăn means "I'm not eating" or "I don't eat it".