'If' statements - 4 kinds:
0 - facts - present simple, present simple
If water boils, the water is a 100 degrees celcius.
1 - real or likely situations - present simple, will + inf.
If a soldier kills the ogre, he will be named champion.
2 - unlikely or hypothetical situations - past simple, would + inf
If I won the lottery, I would go travelling around the world.
3 - situations that cannot be changed - past perfect, would have + pp
If I had studied for the test, I would have passed. (But I didn't study, so I didn't pass.)