Apple TV/TV+
This is going to sound like a dumb question but, do I need to buy the hardware or can I simply purchase the app? Are there differences between the 2?
The Apple TV is hardware. AppleTV + is a streaming service from Apple. See here for devices you can use it on:
All the ways to watch Apple TV+ - Apple Support
It's far from a stupid question. Apple's naming of the hardware, the app and the service just invites confusion.