If you are fuzzy on simple past, look it up in your grammar books; also be sure to check your strong verb charts. Remember that if a verb isn't on the strong verb chart, it is a weak verb!
- The tense which should dominate in the Biography part of your Trimesterarbeit is SIMPLE PAST, not PRESENT PERFECT. That is, you must write "er ging" and not "er ist gegangen".
- In retelling your story, you can choose either simple past or present for the dominant tense. This is something special for retelling literary texts. For example:
Little Red Riding Hood went into the forest. OR
Little Red Riding Hood goes into the forest.
- The most important thing is to be consistent; don't mix tenses.
Why the simple past? The simple past is the past tense used for formal writing. The present perfect is the past tense used for conversation. You are writing formally here, ergo simple past!