In order to form the past perfect tense in German, you need the preterite form of to be/to have (sein/haben) and the second participle of the verb.
As usual, you take sein for verbs denoting a change of state or place, and haben everywhere else.
The preterite forms of to be/to have are the following:
- The second participle for a weak verb is formed by prefixing ge- and suffixing –t to the verb, and for strong verbs you prefix ge- and suffix -en.
- Note that many strong (and mixed) verbs change their stem in the second participle (e.g. gehen – gegangen).
- If the stem ends in d/t, you suffix -et to the weak/mixed verb.
- Do not prefix words with ge- if they end in –ieren, as in studieren – studiert.
You use the past perfect tense for actions before a certain moment in the past. Basically, like in English. I went to the doctor’s because I had been ill for weeks. Ich ging zum Arzt weil ich seit Wochen krank gewesen war.