From support.microsoft.com:
You can upload files and folders from your computer to your OneDrive library or SharePoint team site with the modern experience. You can also browse and upload your files using the classic version. For information, see Differences between the new and classic experiences for lists and libraries.
Notes:
- To create and upload files and folders in a library, you must have contributor permissions to the library. If you’re not sure what permissions you have, contact your SharePoint Admin. For more information, see Types of files that cannot be added to a list or library.
- SharePoint has the ability to upload folders that are built into Microsoft Edge, Google Chrome, and Mozilla Firefox. Internet Explorer doesn’t support uploading folders.