We use will have when we are looking back from a point in time in the future:
By the end of the decade, scientists will have discovered a cure for influenza.
I will phone at six o'clock. He will have got home by then.
or looking back from the present:
Look at the time. The match will have started.
It's half past five. Dad will have finished work by now.
We use would have as the past tense form of will have:
I phoned at six o'clock. I knew he would have got home by then.
It was half past five. Dad would have finished work.
We also use would have in conditionals to talk about something that did not happen in the past:
If it had been a little warmer, we would have gone for a swim.
(but it was cold so we didn't go for a swim)
He would have been very angry if he had seen you.
(but he didn't see you so he wasn't angry)