Advice on Music copyright and business side

I need to understand how the music business works

So I have music that I've done, I've paid for the service bothe producers and singers....then how does the whole royalties work and making a profit...as well as what are the platforms and how do I go about putting it on necessary platforms to make money and where is the best place to put music on for audio books

Copyright- how do I copyright the music and my childrens picture book??

How do I put myself on the best track so I don't get sued or people don't claim my work but everything to do with music...what do I need to know especially in ration to children's picture book publishing

Please do not reply in charge as this will be checked and tracked music