The primary auxiliaries are of three kinds: be, do and have. Each of them has different forms.
The auxiliary be has five forms: is, am, are, was and were. Be also has a present participle (being) and a past participle (been) form.
- I am writing a novel.
- He is working on a project.
- They are playing in the garden.
- We were waiting for the bus.
- He was waiting for her.
Do has three forms: do, does and did. The forms do and does are used to make questions and negative sentences in the simple present tense. Do is used with plural nouns and pronouns. Does is used with singular nouns and pronouns.
- He does not believe in ghosts.
- I do not want to go.
- Does he want to go?
Did is used to make questions and negative sentences in the simple past tense. Note that after do, does and did, we use the infinitive without to.
- He did not go. (NOT He did not went.) (NOT He did not to go.)
Have has three forms: have, has and had. Have and has are used to make the present perfect and perfect continuous tense forms. Have is used with plural nouns and pronouns. Has is used with singular nouns and pronouns.
- I have finished the job.
- She has seen better days.
- We have been waiting for ages.
Had is used to make the past perfect and perfect continuous tense forms.
- She had left before I arrived.
- I had visited them when I was in Mumbai.
Have is also used to talk about possession, relationships and other ideas.
- I have two children.
- She has a pet dog.