I want to port an app to the iPhone (Visual Boy Advance) but I have never written a toolchain application. Could someone point me in the right direction by telling me what they would do?

All I'm asking for is a few sentences.

EDIT: Oh and I am asking for how you would go about porting. I don't want you to say:"Well first learn to use the toolchain." Just assume that I already know how to use the toolchain.

Considering your aim to for a emulator to be ported, we'll assume the following:
1) You've learned to use the toolchain.
2) You've read some of the emulator's source code enough to divide up the execution engine, the graphics processing engine, the graphics output interface (framebuffer), and the user input interface (control pad).

If I were you, I'd follow that up by making a basic iPhone app that contains a text view, which uses the execution engine to run a basic program and output something as a test case.

Then, once the emulated CPU is ported, add the graphics engine/graphics output to either a bitmap file, or to an array which is periodically drawn to the UIView. The purpose here is to see if you got a emulated CPU connected to the emulated GPU.

Once you have that, fix up the output system so you get live graphics output.

Finally, add basic UI so you can do something more than play the entire intro sequence to Mario Bros.