How would I go about creating an iPhone app?

I have a pretty sweet idea for an iPhone app but I have no clue of how to go about making it. Any easy ways, I know most of it is cost I'm assuming. Well thanks.

You can only make an app if you have a macbook.
you will need the Apple iPhone SDK (software development kit) installed. The download link is in the source. Among other things, this kit includes an iPhone simulator that allows you to test your app. This is free but you must know how to program.