A Microsoft file hosting and synchronization service.
If you have a Microsoft 365 subscription with 1TB of OneDrive storage online, log into OneDrive online (https://onedrive.live.com/) and check your storage at the bottom left to ensure you have enough free space on your account online so the files will fit on your OneDrive, because if you go over your allocation online, the files may be deleted.
Then, if you do have enough storage online, by Default OneDrive syncs your Documents, Desktop and Pictures folders on your PC, do not copy the files form your external drive into any of those folders online, because OneDrive may sync the files back down into your C drive.
Create a new folder in OneDrive online for the upload and name it appropriately.
Open that folder.
You can then drag the files from your external drive into the new folder on OneDrive online, and do not interrupt the upload until it has completed to ensure the file transfer has completed correctly.