Sparrow is written in pure Objective-C; you will need to have a basic knowledge of this language to use Sparrow. There are numerous books available that teach you the language, and there is a very good introduction available on Apple's iPhone developer page. If you have not used the language yet, fear not: if you know any other object oriented language, you will get the hang of it quickly.
You don't need to know much about the iPhone API. If you plan to develop your application completely with Sparrow, you won't need to use any UIKit classes at all.
On some occasions, though, it makes sense to intermix Sparrow and UIKit:
Since Sparrow renders its contents into a conventional UIView class and is managed by a UIViewController, any iOS developer will be able to mix Sparrow and UIKit easily.
This manual is covering the 2.x branch of Sparrow. There are some substantial differences between version 1 and 2.
If you create a new project, I'd recommend to use the very latest version of Sparrow. By now, almost all iOS devices that are still downloading content in the App Store satisfy these requirements. Your games will be easier to write and they will run faster.
If you have to support older devices, you can still access the old version here:
Next section: Installation