Need (to): cần

Cần means "need". Put it before a verb for "need to", and before a noun for "need something": Chiều nay em cần đi ngân hàng. I need to go to the bank this afternoon. Tôi cần thêm hai cái ghế. I need two more chairs.

To ask, use có … không as usual: Anh có cần giúp không? Do you need a hand? Answer Dạ, cần or Dạ, không cần. In a shop you'll often hear Chị cần gì không?, which works like "Can I help you?"

Không cần means "there's no need": Anh không cần mang gì hết. You don't need to bring anything. On its own, Không cần đâu is the friendly way to turn down an offer of help.

Cần phải is a stronger "really need to", common when giving advice: Em cần phải nghỉ ngơi. You really need to rest.

Compared with its neighbours, cần says what is necessary, phải says what you have to do whether you like it or not, and nên says what would be a good idea. Mai em phải đi làm is "I have to work tomorrow"; Em nên đi ngủ sớm is "You should go to bed early".