This document discusses the use of should and shouldn't to give advice or express opinions about what is right or wrong. You should means it is a good idea to do something, while you shouldn't means it is a bad idea. Should is used to convey the speaker's opinion, often following phrases like "I think." Examples are given of using should in positive and negative sentences, as well as questions. The document also covers the different types of if clauses - type I for possible conditions, type II for theoretical conditions, and type III for impossible conditions - along with their corresponding main clause forms. Examples are provided of if clauses in different positions and with affirmative or negative sentences.