The document discusses second conditional sentences, which are used to talk about unlikely or impossible future events. It explains that a second conditional sentence has two clauses: an "if clause" in the past simple tense and a "main clause" with "would" plus an infinitive verb. Several example sentences are provided using common second conditional structures like "If I had a million dollars" and "If the weather weren't so bad." The document concludes by posing questions for the reader to practice forming their own second conditional sentences.