Hey Mods 2 Go,
It's awesome you're tackling something that's so new to you. I can tell because overclocking a GBA and overclocking a laptop are nothing alike.
There are oscillators all over a laptop. Modern computers process things asynchronously. That means that different parts of the computer are working on things at different speeds. They all have their own oscillators. But, one could argue that the system clock is the main "oscillator." The system clock tells you roughly how "fast" your computer is. i.e. 2.0 Ghz, 4.4 Ghz, 200 Mhz, etc. This is what manufacturers advertise on stickers on the front of a computer.
A GBA is a way simpler machine. I don't know how to overclock a GBA, but I know GBAs only have one ARM processor with only one speed. If you change the speed of this processor, everything else speeds up the same amount. Everything in a GBA is synchronous. (Maybe audio processing is different. Im not sure here.)
Lastly, overclocking a GBA requires soldering.