Conditional sentences are used to describe things that are not real yet, or that will never be real.
Conditional sentences consist of two parts: the main clause and the if-clause. The if-clause expresses a condition, on which the main clause becomes true or would have become true in the past. There are three different types of conditional sentences:
Type I: real conditions "If the weather is good tomorrow, we will go hiking."
Type II: unreal conditions "If I was a bird, I would fly in the sky."
Type III: unreal conditions in the past "If you had told me before, I would have helped you."
Be careful: NEVER USE "WOULD" IN AN IF-CLAUSE!
To find out more about how to form conditional sentences, take a look at the sub-pages.