How does COBRA actually work?

Quit Amazon last month. New insurance will kick in when I join later next month. I have had doctor visits during the time that I did not have insurance. I have elected COBRA and paid for it but I am getting bills for out of pocket payment. How does COBRA actually work? Do they inform the provider and insurance company that I am now covered? Should I call provider and ask them to “try again” after COBRA kicks in? Should I pay out of pocket and then claim with Premera? Appreciate anyone’s prior experience with this.#insurance #medical #health #cobra

Old TC 300k
New TC 370k