How to say this is my favorite part of the song?
I don't know how to tell them I like this part of the song or even what is the word for favorite?

Question

Answer

좋아하는 것 = favorite (thing)

제가 좋아하는 노래는 부분이에요 
This is my favorite part of the song

Answer

"This is my favorite part of the song"

(그) 노래의 (제가) 제일 좋아하는 부분이에요.  (부분:  part)
(그) 노래 제일 좋아하는 데예요.  (데:  place, spot)  -> more colloquial

Subject is 여기가 (this is) which can be added in the beginning if emphasis is needed.