Zero Conditional is used to describe scientific facts.
Water boils, when you heat it.
“Will” conditional” is used to describe real situations.
If you are not careful, you will hurt yourself.
“Would” conditional is used to describe hypothetical situations.
If I were you, I would take a holiday.
“Would have” conditional is used to describe hypothetical situations in the past as in regret.
If I had known it was a fake, I would not have bought it.
Look at this conditional sentence:
If the President had known that the Private Central Banking System would destroy the nation, he would never have agreed to it but the people who who had put it to him were the same people who had financed his run for the presidency.