The document discusses verb tenses in English. It explains that verb tenses indicate the time of an action through changes in verb form. There are 12 possible verb tenses in English categorized by time frame (past, present, future) and aspect (simple, continuous, perfect, perfect continuous). Each tense expresses a different relationship between an action and time, such as whether an action is ongoing, completed, or will occur in the future. The tenses are formed by combining an auxiliary verb with the base verb form.