If you had already created sync account and synced few the sticky notes from one Windows PC computer, then, on the other computer, to set up, you will need to sign in and download the notes that you had synced from the first computer.
Once you do that, both computers will sync automatically.
But when signing in, any existing data will be deleted. You can export those notes in a file using File->Export option (from Notes Browser), proceed with Sign In and then import those notes using File->Import option (from Notes Browser).
Once each computer is setup, any note you create on one computer will automatically sync and appear on other computer.