The verb 'be' (is/am/are/was/were), 'do' (do, does, did) and 'have' (have, has, had) can be used as main verbs.
For example : - He is a doctor.
Note: They are also called 'helping verbs' as they are used in the formation of tenses, interrogative and negative sentences.
For example :
1. I am dancing with my friend now.
2. Are we going to the mall ?
3. Aman is not coming to school these days.
Following are the uses of primary auxiliaries :
1. Be (is/am/are/was/were) : It is used in the formation of present continuous or past continuous tense.
For example :
1. He is writing a letter.
2. The girl was chatting with her friend.
2. Have (have, has, had) : It is used in the formation of present perfect and past perfect tense.
1. He has brought us frame.
2. I have done my homework.
3. Do (do, does, did) : This form of primary auxiliaries is used in the following ways :-
A. It is used to form the negative of the simple present and of the simple past tense.
1. We donot sleep with the lights on.
2. He didnot complete the given task
B. It is used to from the interrogative of the simple present and of the simple past tense .
1. Does he know the way ?
2. Did he call the police ?
C. It is used to form imperative sentences.
1. Do not write on the wall.
2. Please do complete your home work on time.
D. It is used in question tages when an auxiliary verb is not in present in the statement.
1. I told you to watch out, didn't I ?
2. You like reading, don't you ?
E. It is used to emphasize the affirmative nature of a statement.
1. I do like to watch movies.
2. He does like to go for a morning walk with his mother.