The document discusses the four types of conditional sentences in English: 0 conditional, 1st conditional, 2nd conditional, and 3rd conditional. It provides examples for each type and explains their uses. The 0 conditional is used for scientific facts or general truths. The 1st conditional expresses a probable future result using "will/can + base verb". The 2nd conditional imagines impossible or unreal future situations using the simple past tense. The 3rd conditional expresses past regrets about things that did not happen using the past perfect tense.