If you see some movies in the Apple TV website, does that mean you can watch it if you join some program?
Does that mean if you join some program, such as Apple TV+, then you can watch it as included in the program?


Nope.


  Apple TV+ is said to be included one year free if you buy some new Apple devices, so does that include the movies as listed on Apple TV?


Apple TV+ is Apple's original programming service. The Apple TV+ subscription only lets you watch the original Apple programming for free, which is made available under the service, and not any other media available on the Apple TV app. They have to be purchased/rented separately.

Apple TV app on macOS and iOS/iPadOS now consolidates the iTunes store movies selection, along with Apple TV+, Apple's original programming service.

Starting with macOS Catalina and iOS/iPadOS 13, the iTunes app on macOS which used to let users purchased or rent movies has now been discontinued, and replaced with independent Music, TV and Podcasts apps. Read this Apple Support article to learn more:


What happened to iTunes?


Apple's TV app for macOS is now one stop place to cater to all the visual media consumption available for sale/rent from Apple (which used to be previously made available via iTunes macOS app).

Apple TV+ is a subscription based, original programming service from Apple. A user's enrolment into the service doesn't mean they'll be able to watch any movie made available by Apple for sale/rent for free. So for your case, although the said movie is available on Apple TV, you'd need to pay for it to purchase/rent.

(P.S.: It could be argued that Apple marketing may not have done a good job with making user aware with all the changes that have happened here. The new changes have the potential of leaving a lot of users confused. Here's an interesting take on the same by Daring Fireball, one of the most widely regarded Apple blogger).