I was afraid that you didn't have the disc.
They can be expensive.
Did you buy the iBook used or have you had it since it was new?
If you bought it used, has it ever worked for you, and were any software discs included in your purchase?
Do you know for sure which exact model iBook it is? The iBook 500 MHz came with every type of optical drive you can think of (except a SuperDrive which allows you to write DVDs).
Does this one have a CD-ROM drive (reads CDs), a CD-RW drive (reads and writes CDs), a DVD drive (reads both CDs and DVDs), or a Combo drive (reads and writes CDs and reads DVDs)?
It came with either 64 MB of RAM or 128 MB of RAM soldered to the logic board. If it has never worked properly, the seller may have installed Mac OS X 10.4 (which requires 256 MB of RAM) while the iBook was equipped with enough RAM, and then removed the extra RAM from the one user-accessible RAM slot, leaving it in a non-working state. If you bought it on eBay, some sellers buy a bunch of them from school auctions and load them with Mac OS X 10.4 this way. A Mac should never be sold without the original software discs that came with it when it was new and any upgrade disc(s) for a newer version of the software to which it has been upgraded. That said, it happens quite a lot, and people are left very disappointed. It often costs more to buy the system software and/or RAM to get it working than what it cost to begin with.
If you can let us know a little more about which model you have, we can maybe figure something out.