1) open your resource pack
2) open assets
3) open minecraft
4) create a folder called "sounds"
5) if you need to change the music discs, make a folder inside of "sounds" and name it "records"
5b) if you need to change ingame music, make a folder inside of "sounds" and name it "music"
6) idk about ingame music but for discs you need a .ogg file with a name of one of the minecraft discs. (i.e. chirp, mellohi, 13, ward, etc)
id help further but thats all i know