Need (verb) (without to) is used in negative and interrogative sentences. Also, we can use don`t have to / doesn`t have to / didn`t have to(past), must for the same purpose. In the affirmative, we use need to to express necessity. Modals of necessity example sentences;
- He mustn’t be late for the meeting.
- I must be careful not to upset her.
- They must leave immediately.
- You don’t have to give me money but I can if you want.
- You need to do the exercises, they are obligatory.
- You had to try hard for the match.
- I must study next week.