Step 1: At the bottom right of your screen you should see a cloud icon. Below is a photo showing what the icon will look like. Click on the cloud icon.
Step 2: The OneDrive window will open. At the top right of this window you will see the settings icon. Click on this icon, and then select 'Settings'.
Step 3: Click on 'Manage Backup' under the Sync and backup section.
Step 4: Ensure that all three of the bubbles are toggled on. Documents, Pictures, and Desktop should all be backed up. After ensuring so, you can click 'save changes' and now your OneDrive is fully syncing your data.