The document discusses different types of conditional sentences in English. There are four main types of conditional sentences: factual conditionals which express general truths; future conditionals which refer to possible events and consequences in the future; present unreal conditionals which refer to hypothetical or unlikely present situations; and past unreal conditionals which refer to hypothetical past situations. Each type of conditional has a specific verb tense and structure in the condition and result clauses. The document provides examples of each type of conditional sentence and their typical uses.