Hello and welcome to the support community.
The most common way to get your iBook G3 on the Internet wirelessly, is via the Airport Card which can be installed under the keyboard. This Airport card can be paucashed from online parts stores or via eBay.
Note it's not an AirPort Extreme as that is for the later G4 models.
The only down side to using the Airport card is having the ability to connect to WPA2 wifi's.
if the wifi has a security encryption of WPA2 then it wont work with Airport cards.
The only other alternative is a USB wifi card which plugs into your USB port, however you have a USB 1 port and most USB 2 wifi devices may not be compatible with your iBook.
If you choose this option, I suggest you research the adapter and it's capabilities before your buy it.
Best of luck
The main problem is to find a USB Wifi card with provides drivers for the old OSX 10.4.
If you use a USB 2.0 stick on a USB 1.1. port it will provide a data rate which is slower as specified.
You can use a Wireless Ethernet Bridge, which is connected to the standard ethernet port of your iBook and meets modern standards. The device is stand-alone, work driverless and is configured via browser-interface. They are mainly made for Xbox and other gaing devices or TVs but will work with your iBook too.
You may consider to max out your RAM from 256MB to 640MB. A 512 MB RAM stick costs less than 20$ nowadays.