Verify that OneDrive is running by clicking the Windows key, typing "one" then launching the OneDrive application.
Once OneDrive is running, right click the blue cloud icon in the system tray at the lower right and select settings.
If you want to make sure your files are always available even when working offline, click the settings tab and make sure "Files-On-Demand" is unchecked. Note that this may result in running out of hard drive space.
Click the backup tab then click the "Manage backup" button
Turn on backup for desktop, documents, and pictures by checking the checkboxes then clicking the start backup button.
Close OneDrive settings.
OneDrive will stop syncing anytime you change your password or after about 3 months. Verify it is still syncing by checking that the OneDrive icon doesn't have an X through it. To re-enable syncing, click the OneDrive icon and sign back in.