Tense indicates the time or continuation of an action in relation to the time of speaking. The main tenses are past, present, and future. The past tense refers to events that occurred before now. There are several types of past tenses including past simple, past continuous, past perfect, and past perfect continuous. The past simple describes completed actions in the past, the past continuous describes ongoing actions in the past, the past perfect describes actions that occurred before other past actions, and the past perfect continuous describes ongoing actions up until some point in the past. Each tense uses different verb forms and structures to indicate the specific relationship between the action and the past.