auxiliary

 

used with the present participle of other verbs to describe actions that are or were still continuing

Where are you going?

 

used with the present participle of other verbs, and sometimes after a modal verb, to describe actions that will happen in the future

I'm going to France next week.

 

used with the past participle of other verbs to form the passive

He was injured in a car crash.

 

used in conditional sentences to say what might happen

If he were to offer me the job, I'd take it.

 

used to say that someone must or should do something

You are not to see him again.

 

used to show that something has been organized

They are to stay with us when they arrive.