Learn Turkish: Bu evin tek kapısı var. - This house has a single door.

In Turkish, to say that someone or something "has" something, we build a sentence that literally translates to "the house's door exists". The -in suffix on ev (house) makes it mean "of the house" or "the house's".

Why does kapı (door) have the -sı suffix?

The -sı is a possessive suffix meaning "its". Because we established the owner as evin (the house's), the thing owned must match it. So kapısı means "its door". Together, evin kapısı means "the house's door".

How does var mean "has" in this sentence?

Turkish does not have a direct verb for "to have". Instead, you express possession by saying that an owned thing exists using var (there is / exists). The structure evin ... kapısı var literally translates to "the house's ... door exists", which is the standard A1 way to say "the house has a door".

Could I use bir instead of tek?

Yes, but it changes the focus slightly. Bir kapısı var simply means "It has a door" or "It has one door". Using tek specifically emphasizes that it has a single door and no more.