Use a document library to store, organize, sync, and share documents with people. You can use co-authoring, versioning, and check out to work on documents together. With your documents in one place.
Document Library is a place on the site where you can create, collect and update files with other members in SharePoint. If you cannot access the document library, you have to obtain permission from the administrator of the site to access the library.
A document library provides a secure place to store files where you and your co-workers can find them easily, work on them together, and access them from any device at any time. For example, you can use a document library on a site in SharePoint Online to store all files related to a specific project or a specific client. Adding files or moving files between folders is as easy as dragging and dropping them from one location to another. You can read more about document library in sharepoint, here.
Questions having the tag document-library regards the use, design, configuration, and implementation of a document library in SharePoint.