 Have to 
We use have to when we want to say it is necessary to do something. Many people use have got to or need to when speaking. They are used the same way as have to. Have to is always followed by the base form (infinitive form) of the verb. For example: I have to study for the test.
I've got to study for the test.
I need to study for the test. In the present tense, have to always has the same form, except for the 3rd person singular (he, she, it), when it becomes has to. In the past tense, have to changes to had to, and doesn’t change for any of the subjects. In the future tense, have to becomes will have to, and doesn’t change for any of the subjects.
To make a Wh- question, we add the Wh- word before the Yes/No question. For example: Where will we have to be at 9 o'clock?
When does she have to decide?
When who or what is the subject of a question, we don’t use a subject pronoun. In the present tense, the verb is always singular (like with he, she, it) and doesn’t take a helping verb (do, does or did). For example: Who has to walk the dog?
What had to happen? Who will have to catch the train? | ||||||||||||||||||||||||||||||||||||||||||||||||||