The first of these components is:
The form: is the structure of the music, it's more like a journey that will make your mood go up and down. We mean by the form, the intro, the verse, the chorus...et, each of these form components has its own destinction from others and also has its own mood.
The melody: it's the musical part of any song, it has to be unique, strong and has to leave an impact on the listener. This melody has to go along with the music form that we have talked about.
The harmony: We mean by harmony chords, chords are combination of notes played together in the same time, chord sequences are very important in music especially western music.
Lyrics: You all know what is this, lyrics are the word part of the song, it has to be compatible with the song melody, theme, harmony as well as the song form that you've chosen. Writing song lyrics isn't hard as most people say it is, not if you have the right songwriting techniques.
These components together will make you a great song, but what if you want to make your song not just great but a song that sticks in your listeners memories, well that way you have to find a good:
Hook: There is no exact definition of the hook but i'll give you a simple one. A Hook is the part of music that stays in the listener's mind. Sure this happened to you if you are human :) , where you listen to a song and stay singing that part "the hook" of the song all day long!!!
Well that's it, it's not complicated after all, these parts alltogether, when they have been taken care of carefully will make you a great and memorable song.