The document discusses different types of conditional sentences in English:
1) Zero conditional - Used to talk about things that are always true. They use the present simple in both the if-clause and main clause.
2) First conditional - Used to talk about things that are possible in the present or future. They use the present simple in the if-clause and will + infinitive in the main clause.
3) Second conditional - Used to talk about unreal things in the present or future. They use the past simple in the if-clause and would + infinitive in the main clause. When using be, we must use "were" instead of "was" for all subjects.