While I bet if I searched I could find this documented in the Microsoft site, Windows has so many features that go unnoticed as well as no "official" manual. Windows 10 is also a version they roll out upgrades that may introduce new ideas like the one you found.
So for this one you can either research on the web or Try David Pogue's "The Missing Manual" book titles but my view is to not fret too much about this.
Me? I tend to unpin all those tiles. Not very useful for me.
I recently discovered that on the start menu tiles display I could now nest tiles into a "tile folder". Exactly like an iPhone I can click and hold the mouse on a given app tile and then drag it over another app tile and hover above it for about a second. The two tiles now "merge" into a single tile with each tile's picture appearing in miniature with the new "folder" tile. If I click on the folder tile the tiles it contains drop down for use and the "folder" tile changes to an up arrow (carrot symbol). If I click on the folder tile's up arrow the tiles it contains are removed from the screen and put back into the "folder" tile.
The "folder" tile is deleted when all apps are dragged out of it.
When was this feature added? Are there any instructions on how to use it?
The first time this happened to me was by accident and I thought something broke.
The feature does conserve app tile space on the screen and is easy to open the folder tile.
Any additional information you can added and also provide a link to microsoft windows 10 support that describes this feature? I so far I have not been able to find any info?