Private folder on hd - terminal command help

[Sivs]

When I downloaded onedrive from microsoft, then suddenly, an additional 33GB was added to my mac and it turns out that it is stored in the 'private' folder, that has to be flagged/hidden or something like that. I did some research and found that I had to type the command 'sudo chflags hidden /private/' in terminal (I must admit I'm bad with computers, so might have done it wrong) but it does not work!
Any help please, I have tried for hours to fix this problem.

-Siv

 

[grahamperrin]

The first screenshot shows around 30 GB in the private temporary folder for a user. At a glance, one file in that area is massive; that's unusual.

1. Perform a safe boot
2. after the progress bar, OS X will present the login UI
3. refrain from logging in
4. restart.

OS X: What is Safe Boot, Safe Mode? – Apple Support

A safe boot should, in most cases, silently repair file system inconsistencies; and will probably deal with those temporary files.

Then use Disk Utility to repair permissions …