What is the charge of $4.99 for Apple TV relate to?

That entitles you to watch all Apple TV+ content for no additional charge. See https://tv.apple.com/

It does not include Apple TV content that is not part of Apple TV+

And just to remind you, you have to sign up for that subscription, it doesn’t not automatically start for no reason. You may have been offered a free trial that became a paid subscription if you did not cancel it after the trial period.