You need to enroll in the Apple Developer Program in order to publish your app to the App Store. You can read more about developer program and its options here.
App Store Connect is a web-based tools kit for controlling apps sold on the App Store. As a member of the Apple Developer Program, you will set up your app name, description, screenshots, submit and manage apps, invite users to test with TestFlight, monitor sales reports, and more.
Tip: You can review the App Store Connect tutorial for a more detailed overview.