Ответ:
1. After he had finished school, he went to a camp.
2. As soon as she had phoned her friend, she went to meet her.
3. I read the book after I had seen the film.
4. I had cleaned my room before I invited my friends home.
5. He entered the university after he had finished school.
6. Не told me about his impressions after he had returned from his journey.