Complex sentence: It has been awarded since 1959 and unlike the Record of the Year award, which goes to the performer and production team of a single song, Song of the Year goes to the composer (s) of the song.
Split into simpler sentences: It has been awarded since 1959 to the composer (not the performer) of the song in question. Unlike Record of the Year, which goes to the performer and production team of a single song, Song of the Year goes to the composer (s) of the song.