have1 S1 W1 past tense and past participle had third person singular has
used with past participles to form perfect tenses:
Our guests have arrived.
Has anyone phoned?
We've been spending too much money.
I hadn't seen him for fifteen years.
'I hope you've read the instructions.' 'Yes, of course I have.'
You haven't done much, have you?
used to say that someone should do something:
You'd better phone to say you'll be late.
We'd better not tell Jim about our plans just yet.
if someone had done something:
Had we known about it earlier, we could have warned people of the danger.