Turkish has two past tenses. The -di past is for what you saw or know first hand. The -miş past is for what you heard, inferred or only realised later: gelmiş means apparently he came. Stories and hearsay use -miş throughout.
Examples
- Dün İstanbul'a gittim.
- Yesterday I went to Istanbul.
- Duyduğuma göre çok güzel bir yermiş.
- From what I heard, it is a very beautiful place.
- Yağmur yağmış, yerler ıslak.
- It must have rained, the ground is wet.
The mistake to avoid
Using -di for something you did not witness sounds like a false claim.
Where this fits in
Geçen hafta sonu, Turkish A2: Talk about the past: yesterday, last weekend, and travel memories.