The document explains the three types of conditionals in English - the first, second, and third conditional. The first conditional uses "if + present/will" to talk about likely future events. The second conditional uses "if + past/would" for unlikely future events. The third conditional uses "if + past perfect/would have" to talk about hypothetical or imagined situations in the past. It provides examples of each conditional and exercises for the reader to practice forming third conditional sentences.