The past tense is a grammatical form used to describe actions or events that have already happened. It indicates that something took place before the current moment. For example, in the sentence "She walked to the store," the verb "walked" shows that the action is completed. There are several types of past tense, including the simple past, past continuous, and past perfect. The simple past is used for actions that occurred at a specific time, while the past continuous describes actions that were ongoing in the past. The past perfect indicates that one action was completed before another past action, as in "He had finished his homework before dinner."