have作为助动词可以：
1.构成完成时态(have+过去分词)：
What has happened?
出了什么事?
He told me Jane had left．
他告诉我简已经走了。
She will have arrived by this time tomorrow.
明天这时她就会到了。
How long have you been there?
你在那里待了多久?
2．构成完成进行时态（have+been+现在分词)
We have been trying to contact you．
我们一直在想和你联系。
She has been teaching there for thirty years．
她在那里任教达三十年。
That was the book he had been looking for.
这是他一直在找的书。
另外，have (got)to还可构成谓语，表示“不得不”：
We have(got)to be careful．
我们得小心。
You don’t have to worry．
你不必忧虑。
