have to - don't have to

    

Have to is used with  I, you, we, they (in affirmative sentences)

Has to is used with he, she, it (in affirmative sentences)

Don’t have to is used with I, you, we, they (in negative sentences)

Doesn’t have to is used with he, she, it (in negative sentences)

For questions we use “do / does + subject + have to"

We use “had to” to express obligation in the past

Exercise 1 
Exercise 2
Exercise 3