In the (Apple) menu at the upper right you will find Software Update. Selecting that will update your iBook with the latest software from Apple.
If you have its original System and Applications Installation CDs take good care of them. If you don't try to get them from whomever gave you the iBook. These discs are your only salvation in the event you need to reinstall its original operating system (probably Panther). Since it was upgraded to Tiger you need that disc too. Don't misplace them.
The iBook was a nice computer in its day but is just about prehistoric in computer terms. It will be useful for basic tasks but not much else.