Let me add my two cents to what Torsten has stated.
As regards the use of tenses, both past simple and past perfect can be used in a single sentence in which you might want to refer to two activities, one having taken place earlier than the other. In such a situation, you are required to show the first activity (past in the past) in the past perfect tense construction as in the following examples.
When I went to the cinema, the film show had started. (Here, I could not reach the theatre before the film show began)
The thief had run away when the police arrived. (Here again, the police were late, and they reached after the thief left)
Further, you should use only the past simple when the activity is reported as having taken place at a specific time in the past as in the following examples:
- The Prime Minister visited the gulf countries last month.
- Shakespeare was born in the year 1564.