Which tense is used to describe an action that happened before another action in the past?

Which tense is used to describe an ongoing action in the past?

Which tense is used to describe an action that happened before a specific time in the past?

Which tense is used to describe an action that had already happened when another action in the past occurred?

Which tense is used to describe an action that started in the past and continued up until another point in the past?