To get started with Autosync for OneDrive, you'll first set up the application and then connect your Microsoft account to the app:
Install OneSync: Autosync for OneDrive from the Play Store on your Chromebook and open the application.
Click I agree to accept the terms and conditions of the app.
Click Allow to allow OneSync access to the files on your device.
Click Connect to OneDrive. and Enter your Microsoft account credentials in the next screens.
Click Sign in at the end to finish the process.
When asked to let this app access your info, click Yes.