There are several components to the Federal No Surprises Act. A GFE (good faith estimate) is used for self pay, or out of network, or any patient who asks, so they know PRIOR to services being rendered what the approximate cost would be. Most practices would collect that at the time of service. The practice determines their fees, and the patient is required to pay for them. There are several requirements as to when the GFE is provided.
Another separate component is for patients who are unknowingly receiving out of network services, or receiving out of network in an emergency.
Like you were on vacation in Oregon, had severe chest pain and went to the ER. If that Oregon hospital/ER provider is out of network, your HMO must still cover the service.
Or you went to an in-network hospital, had an in-network surgery. During the surgery, you had an abnormal EKG and cardiologist was called in. If that cardiologist was out of network, your HMO must cover. You did not make the choice to receive that out of network care.
For some states, there were already laws regarding this in place, and it's a minimal change. In other states, there were less prior regulations so the federal law created a lot of changes.
Depending on where you work and your role, that should guide how much of this you really need to know vs just be aware of. Here are some starting references: