You may want to keep some files offline (on your device) as well as online in case you do not have Internet access when you want to work on them.
- Open File Explorer
- Go to the files you want to be available offline.
- Select individual files or folders.
- Right-click and select
- Check the status column for a green checkmark to make sure it is done downloading.
Additional information at Microsoft can be found here.
Microsoft has free training on OneDrive here.