A Microsoft file hosting and synchronization service.
There are a few ways to do this, and the best option depends on the type of accounts involved and how many files you need to share.
How many files are you planning to move or share?
If it is only a small number, the easiest method is usually to download them manually from OneDrive on one account at www.onedrive.com, then sign in to the other account and upload them through OneDrive online there.
If it involves a lot of files -
If one account is personal and the other is work/school account, it is best to install the OneDrive desktop app. In the OneDrive settings, you can go to account tab and add another account. You can run two OneDrive app instances side by side, gray cloud for personal and blue cloud for work/school. In File Explorer, you can move files from OneDrive - personal folder to OneDrive - business folder.
If both accounts are work/school accounts, above method also applies.. and you will have two blue cloud icons on taskbar. Two business folders in File Explorer and you can move files between.
If both accounts are personal, you cannot run two OneDrive instances. You will have to right click on the files you want to move, use "always keep on this device". Wait for them to download - turn solid green for the status icon. Then in OneDrive settings > accounts > unlink this PC, relaunch OneDrive, sign into the other personal account to allow the files to sync to the other personal account.