You can upload files to a document library in SharePoint by dragging them from your computer and dropping them into the document library.
Note: Upload files to a library covers the classic experience.
Drag and drop to a document library
Open the document library where you want to upload a folder or files.
Select files or folders on your computer and drag and drop the folder or files onto the document library page.
Important: Internet Explorer 11 does not support uploading folders.
If you are uploading large files--or many files that add up to a large total size--to a document library, you may get errors due to the file size limit in SharePoint Online or timeout errors in your version of Internet Explorer. Steps you can take to get around these errors include:
Upload 100 or fewer files at a time when using drag and drop.
Avoid uploading files larger than 15 GB for SharePoint Online which is the maximum file size by default.
For file sizes exceeding 15 GB, if you see a "Working on it" message that never goes away, follow the instructions in Microsoft Support: Internet Explorer error "connection timed out" when server does not respond.
Some file types in the document library are blocked for security reasons. For more details on blocked file types, see Types of files that cannot be added to a list or library.
Some document libraries have restrictions that can limit how many files you can upload at a time. For example, if your document library has been set up to require a specific content type, or require a specific field, you can only upload one file at a time.
If you don’t see the option to drag and drop files, update your copy of Office.
Sometimes site administrators set up additional requirements in a document library that you might have to work with. These requirements can include:
Require check out: Site owners can set up a document library to require you to check out files before you edit them (and check them in when you finish). If your document library requires check out, the file is checked out to you when you first upload it. You have to check the file in before other people can edit it. To learn about checkout, see Check out or check in files in a document library.
Track file versions: You can add replace an existing file with a revised version of a file. If the document library is set up to track versions, you can add the revised file as a new version, which becomes part of the version history of the file. If you are uploading a new version of a file, consider typing comments about what changed in this version so that you can more easily track the history of the file. To learn more about versioning, see How does versioning work in a list or library?
Fill out file properties: When you add a file, folder, or link to a document library, you may also be required to fill out a form (in the information panel) with information about the item, such as its description, a department name, or a project number. To learn more about editing information about a file, folder, or link, see View and edit information about a file, folder, or link in a document library.
Approve submitted content: Site owners can set up a library to require approval of the content before it becomes visible to others who use the library. As the author, you can see the file listed and work with it, but nobody else can. For example, a legal department might require approval before documents become public. To learn more, see Require approval of items in a site list or library.
A word about uploading folders and browser versions
SharePoint takes advantage of the ability to upload a folder that is built into Microsoft Edge, Google Chrome, and Mozilla Firefox. Internet Explorer doesn't support uploading a folder.