There are two past tenses in Turkish. One of them is görülen geçmiş zaman (seen or direct past tense) and the other one is duyulan geçmiş zaman (heard, indirect, reported or inferential past tense). Their names may vary according to different sources. But the main point is that the first one is used for events that you have witnessed, you have seen when the action was taking place, and the other one is used for actions that you haven't witnessed, you have heard from somebody else. Görülen means seen and duyulan means heard.
Appropriate form of the suffix –di (it changes according to the vowel and consonant harmonies) and the personal ending are added to the verb stem. An important thing to note here is that the personal endings are different from most other tenses.
Verb stem + appropriate form of di + personal ending