Free movies

Movies that say rent or buy are from the iTunes Store and not free. 

Your subscription is for Apple TV + 

Apple TV + is Apple Original content. It’s a channel found within the Apple TV App. The shows included in your subscription will have the tv+ logo on them - those are free. This is not like Netflix or Prime etc,  where all is included in the one App.  

That offer is for Apple TV Plus, which is a service for Apple originals. It currently has 10 series and 2 movies, with more added each month. You can scroll down to Apple TV Channels and select the Apple TV + icon to see exactly what is included with that service.

It does not entitle you to content from the iTunes store, which is from 3rd party providers and done via rental or purchase.