Describe the formation and usage of the past continuous tense.

The past continuous tense, also known as the past progressive tense, is formed by using the past tense of the auxiliary verb "to be" (was/were) followed by the present participle (-ing form) of the main verb.

The formation of the past continuous tense is as follows:

Positive:
Subject + was/were + present participle

Negative:
Subject + was/were + not + present participle

Question:
Was/Were + subject + present participle?

For example:
- Positive: She was studying all night.
- Negative: They were not playing football.
- Question: Were you sleeping when I called?

The past continuous tense is used to describe an ongoing action or event that was happening in the past at a specific time or over a period of time. It emphasizes the duration or progress of an action in the past.

Some common uses of the past continuous tense include:
1. Describing an action that was in progress at a specific time in the past: "I was cooking dinner at 7 pm yesterday."
2. Describing two ongoing actions happening simultaneously in the past: "While she was studying, he was watching TV."
3. Describing an action that was interrupted by another action in the past: "I was reading a book when the phone rang."
4. Describing a background action or atmosphere in the past: "The birds were chirping, and the sun was shining."

It is important to note that the past continuous tense is not used for actions that were completed in the past. For completed actions, the past simple tense is used.