A music publisher is simply in the business of handling and exploiting musical compositions (aka musical works/songs).
This includes, but is not limited to:
And generally sourcing opportunities for the songwriters they represent.
Record companies deal with sound recordings OF music works, not the musical works themselves.
At the very least, if you are a songwriter, you need to make sure you are collecting all the publishing you are owed.
If you haven’t been approached by a publisher, you can use a publishing admin service to handle that side of the business for you.
The source code for the frontend of this website is available on GitHub.