The 2nd conditional is used to talk about things in the future that are probably not going to happen. A dream or an unrealistic wish, for example.
Form the 2nd conditional by using the Past Simple in the if-sentence and "would" in the main sentence. For example: If I won the lottery, I would buy a new car.
You can also reverse the sentence, just as with the 1st conditional: I would buy a new car if I won the lottery.