I have an Apple TV "device". Do I still need to pay for Apple TV $5/month?

An Apple TV device (or a Roku or other devices) allows you to access Apple TV. The monthly subscription charge is for Apple TV+ (note the "+") which is Apple's streaming service. You would only need to pay for that if you want to view Apple TV+ content. See the following for what is available on Apple TV+ https://tv.apple.com/

There's no charge to use an Apple TV box, or the Apple TV app, the$5.00 (4.99) is for a subscription to "Apple TV +" (note the +) this is Apple's own subscription channel to watch Apple's original media.