I moved your post from the Off Topic folder, since I assume you are asking about Tune-up in Windows Live OneCare.
Tune-up does the following:
1. Defragments the hard disk - that is, joining file fragments together so that they are contiguous on the drive.
2. Performs a complete scan for viruses and spyware
3. Performs a Disk Cleanup if you configure it to do this task
4. Executes a backup or prompts you to perform a backup if you have scheduled it to occur with Tune-up
5. Confirms that your PC has all available critical and important Microsoft updates for Windows
You can learn more at http://onecare.live.com
-steve