Yes, all the videos where they create full scenes are done by either purchasing assets on the Marketplace and using those, or by creating your own assets from a 3d modeling program such as Maya, and importing them as FBX. Also there is a lot of free content/assets to use from things like the Kite Demo (Open World Demo Collection) and now the Infinity Blade packs, and a few others but I haven’t looked into all of them and I’m not sure if any of them contain much interior-related assets. As far as where you should go next, I can only say what I’ve been told and what I see being answered all the time, and that is to just “start a project and dive in” basically. I’d let someone else answer that question in a more in-depth manner, though, since I’ve only really just started myself.