The document discusses conditional sentences, specifically the second conditional. The second conditional expresses less probability that an action will occur, though it is not impossible. In the second conditional, the if-clause uses the past simple tense while the main clause uses the modal verb "would" plus an infinitive verb without "to". Examples are provided such as "If I had a map, I would lend it to you" and "If I were you, I wouldn't do that". The document also provides a homework exercise with 15 sentences to complete using the correct verb form for the second conditional.