From the drop down menu where your profile pic is (top right), find the "Folders" option. Click that. Or you can also go to: https://toyhou.se/~folders 

You'll see all your folders on the right hand side. Click the one you want to display like mine in your screenshot. The General Settings will show up. Find the "Folder style" option menu (lower right) and choose "Flattened (Single page folder)". Now, any sub-folders within that folder will have their contents displayed under the sub-folder name within that main, flattened folder.

I hope that helps. Good luck!