HI!

Thanks for the reply, I should have added some context. The song is Mercy by Shawn Mendes, the Key is E minor. The chords being used are E minor, G Major, b minor and A Major. Attached is a link to the sheet music I'm looking at and I was wondering if someone can give me a explanation just for the first 4 bars of how the non chord tones are being approached and why everything is working together the way it is.

https://www.musicnotes.com/sheetmusic/mtd.asp?ppn=MN0168128

The confusion I have with non chord tones is that I don't know why they are working together with the notes in the current chord being played as well as non chord tones being held going into another chord.

I don't plan on going really hardcore with the theory but this is something I want to understand since I feel like it will be useful to know why the music is fitting together.