As described in About favorites, you can mark folders and files as favorites for quick access. When you mark a folder as a favorite, all subfolders and files in that folder are also marked as favorite.
To mark a folder or file as a favorite, navigate to that folder or file. Open its contextual menu by tapping () to the right of the folder or file. In the menu, tap Favorite. The folder or file icon appears with an orange star.
To remove the favorite status, tap the contextual menu for the folder or file then tap Unfavorite. For example:
The orange star is removed from the folder or file icon and it no longer appears in the list of Favorites.
If you are configured to access SharePoint sites or network shares, you can mark as favorites the files and folders in those accounts. As described in About SharePoint and network share accounts, the folders and files in each account are separate from each other. Favorite folders and files within one account do not appear in the other accounts’ Favorites.