CMS trial - 14 days should be more than enough to play with it. Also, its $20/month after that so it's not like it's a huge commitment.
Enable for templates - If you go to the Marketplace in the builder > Integrations > three dots > Open Project. You can see CMS in action there.
Content - I've made a lot of in depth tutorials on CMS and the builder. Of course there can always be more, but here's a full playlist of CMS tutorials
https://www.youtube.com/playlist?list=PL4vVqpngzeT6zVt2Jrsx3v1e0z3gq15O4Everything you need to know about CMS should be in there, especially if your goal is to see how it works