It would be great if we could add already created pages to folders. Page folders exist but you need to create a new page from scratch.
You can. At the bottom of the inspector tool for the page you can choose the page folder.
Hope that helps! 
For All Your No-Code Education Needs:
- One-on-One Tutoring
- eLearning Hub
- Video Tutorials
- No-Code Classes
Ohh thanks, it was hidden plain sight 
Yeah. It’s definitely not something you notice right away. 