For new devices activated after July 1st, 2021, the offer has changed into a 3 months offer.
The offer is for Apple TV+. Apple TV+ is Apple’s streaming channel featuring Apple Original content. Other content through the Apple TV box and/or the Apple TV app will have to be payed for separately.
The offer has to be redeemed in order to get it: find the “Enjoy <x time> Free” button in the TV app.
The regular price after the promotional offer period depends on country and currency. E.g. USD 4.99/CAD 5.99/AUD 7.99.
Read here how to redeem: Apple TV+ offer - Apple
Read here about the conditions: Apple TV+ offer - Terms and conditions - Apple
Read here if you have trouble redeeming: If you can't redeem your promotional trial of Apple TV+ - Apple Support