1. It was early morning. Ben had written his composition by that time. 2. She saw that the prairies stretched for miles. 3. When we came back to the camp, the sun had risen. 4. Susie had looked through the letters before her elder sister got them. 5. He saw a stranger stealing his bike. 6. Ted suddenly remembered that he had forgotten to buy some bread. 7. By the end of the year they had got ready for their exams. 8. Sam read the book and then did his homework.

It was early morning. Ben had written his composition by that time.
The sentence is in the past perfect tense. It indicates that the action of writing the composition was completed before another action or point in the past (the early morning).

She saw that the prairies stretched for miles.
The sentence is in the past simple tense. It describes an event or observation that happened in the past, with no indication of its relationship to another action.

When we came back to the camp, the sun had risen.
The sentence uses the past perfect tense ("had risen") to show that the action of the sun rising occurred before the action of coming back to the camp in the past.

Susie had looked through the letters before her elder sister got them.
This is in the past perfect tense. It highlights that Susie's action of looking through the letters happened before the elder sister received them, both actions occurring in the past.

He saw a stranger stealing his bike.
This sentence is in the past simple tense. It describes a completed action in the past (seeing the stranger) and the ongoing action (stealing the bike) that was happening at the moment he saw it.

Ted suddenly remembered that he had forgotten to buy some bread.
The past perfect tense ("had forgotten") is used to show that Ted’s forgetting to buy bread occurred before his sudden remembrance, both actions happening in the past.

By the end of the year they had got ready for their exams.
This sentence uses the past perfect tense ("had got ready") to show that their preparation for the exams was completed before the specified time (the end of the year).

Sam read the book and then did his homework.
The sentence is in the past simple tense, describing two sequential actions that occurred in the past: Sam first read the book, and then he did his homework.