Commas can be used to contrast opposites in a sentence written in phrase form, as in "The tutor was very friendly, not mean and scary the way Peta expected." Commas are also used to separate elements in a list and parts of a sentence introducing direct speech, such as "This is my favourite story, Peta told her tutor." However, commas should not be overused as it makes the writing difficult to read, similar to overusing full stops. The document provides examples of correct comma usage and a warning against overusing commas.