Auxiliaries
Auxiliaries are verbs that do not carry meaning on their own. They stand together with main verbs and give information about tense, simple or progressive, as well as on active or passive voice. To learn more, go to main verbs!
The verbs "to be, to do" and "to have" can be both auxiliaries and main verbs.
If they stand together with another main verb, they function as auxiliaries.
- I have a car. (Vollverb)
- I have left my jacket in the house. (Hilfsverb)
To Be
The auxiliary "to be" can occur in the following constructions:
form of "to be" + progressive 
The children are dancing.
The children are dancing.- The man is reading a book.
- The phone was ringing.
form of "to be" + passive This car was made in Germany.
This car was made in Germany.- This story was told to me by my grandfather.
- This book is written in English.
To Have
The auxiliary "to have" can be used as follows:
form of "to have" + present perfect or past perfect he has arrived, he had arrived
he has arrived, he had arrived- I have made dinner. (present perfect)
- He had known that before. (past perfect)
To Do
You need the auxiliary "to do" to ask or negate questions in simple present and simple past:
- Do you like ice cream? Yes, I do.
- Do you have a watch? No, I do not/don't.
- Did you enjoy the film? Yes, I did.
- Did you go to your lessons this morning? No, I did not/didn't.
The auxiliary "to do" can be very useful if you want to answer a question shortly: If someone asks you a Yes-No-Question, you can simply reply "Yes, I do" or "No, I don't". This is called a Short Answer.
You also need "to do" for the negated imperative:
Don't run so fast!
Be careful with using contracted forms (short forms) like "I'm" or "didn't" in written texts. In spoken language you use them all the time, but in a written text, they might look informal!
In the following exercises you should take a look at all the sentences and decide whether the verbs "to have", "to do" and "to be" are used as a main verb or an auxiliary.