Learn Turkish: Kapının kolu çalışmıyor. - The handle of the door is not working.

The suffix -nın shows ownership, similar to English "of" or "'s". Because kapı (door) ends in a vowel, we use the buffer letter n before adding the genitive suffix -ın. This makes it "the door's" or "of the door".

Why is there a -u at the end of kolu?

In a Turkish possessive phrase (X's Y), both words get a suffix. After we put the genitive suffix on the owner (kapının), we must put a possessive suffix on the owned item. Here, kol (handle) gets the suffix -u because of vowel harmony, making kapının kolu (the door's handle).

Does kol usually mean "arm"?

Yes, kol literally means "arm". Turkish often uses names of body parts for inanimate objects, so the "arm" of the door is its handle or doorknob.

What are the parts of the verb çalışmıyor?

It starts with the verb root çalış (work). Next is the negative suffix -mı (meaning "not"), and it ends with the present continuous tense suffix -yor (meaning "is doing"). Put together, it means "is not working".