I am SUPER confused

Okay so, I want to make a custom Background music, I know how to do Random number I think, but whenever I try to see! They NEVER make it make sense, never explain what happens, what to do, I'm using 2020.2, not up to date Mcreator, and whenever I try searching for my answer, no one shows how to make it so that only the PLAYER can hear it, I want the player to always hear it until it finally ends, I want them to hear it as they move somewhere else, I will go into more detail if I don't understand what your talking about or you don't know what I'm talking about,