(if + present simple, ... present simple)
If you heat water to 100 degrees, it boils.
(if + present simple, ... will + infinitive)
If it rains tomorrow, we'll go to the cinema.
(if + past simple, ... would + infinitive)
If I had a lot of money, I would travel around the world.
(if + past perfect, ... would + have + past participle)
If I had gone to bed early, I would have caught the train.