Coinsurance, however, applies to the fees accumulated during the visit, excluding the copay. You'll have to check your policy to see exactly which services copays and coinsurance apply to, but generally, coinsurance will apply when more expensive things, such as testing, are involved.
Sometimes, you'll pay only coinsurance, such as when you have an MRI planned at the local hospital. Other times, you'll pay only a copay, such as when you visit your doctor for a medication change but no lab work. Sometimes both will apply, like when you're visiting your doctor and need an X-ray.