How to backup to Onedrive

[Peter Kinross]

I wanted to backup to OneDrive. Started the app it selected the folders to back up and it told me that it would add 245 GB to my C: drive! ! ! A bit weird for backing up to the web.
Question: How do I back up to OneDrive on the web ONLY, leaving the files on my computer and NOT storing the backup on my computer. I phoned MS and put this question to them, they responded that there would be a charge for that help. Seriously!
So much for the amateurs at MS, now to get to the pros at the Lounge onto it.
Can anyone answer that question?