The past perfect tense indicates that one action in the past was finished before another action in the past. You form the past perfect using had+past participle. I had washed my hair before I went to work. I had finished eating by the time the film started. "By the time" is a time phrase that is commonly used with the past perfect. It means-the first action was finished at an unspecified time before the second action was finished. I hope this helps. :)

1. When he had finished his homework, he went to dinner. 2. John said that Mili had bought a new motorcycle