You can use libraries to access files from one convenient place, regardless of where they’re stored. In some ways, libraries are like folders: you can organize, share, and view files in them in the same way. For info about doing these kinds of things in File Explorer, see How to work with files and folders. For info about searching in File Explorer, see How to search.
Unlike folders, libraries gather files that are saved in several locations instead of actually storing your items. For example, the Documents library lets you access documents that are actually saved in the My Documents and Public Documents folders.
There are four default libraries (Documents, Music, Pictures, and Videos), but you can create new libraries for other collections. You can also add and remove folders from libraries. For more info, see Libraries: How to add or remove a folder.