If I go home, I will have lunch If I went home, I would have lunch If I had gone home, I would have had lunch.
If you drink a lot of coffee, you have problems with your heart. Или: If you drink a lot of coffee, you will have problems with your heart. — Если ты пьешь много кофе, у тебя будут проблемы с сердцем.
If I had money, I would buy a flat. — Если бы у меня были деньги, я бы купил квартиру
You could read the whole book, if you wanted. — Ты бы мог прочитать всю книгу, если бы хотел