The iOS Software Development Kit (SDK) provides support for developing iOS applications and includes the complete set of Xcode tools, compilers, and frameworks for creating applications for iOS and Mac OS X. These tools include the Xcode IDE (its integrated development environment) and the Instruments performance analysis tool, among many others.

Xcode 4.5 (the latest version) is now an application you simply download from the Mac App store. (You will need OS X 10.7.3 or better.) You should also become a registered developer.

To do that, first go to the iOS Dev Center site, look for (and then click) the link to become a registered developer, fill out some registration information, and then start reaping the benefits of being a registered developer, starting with access to tons of documentation sample code and a lot of other useful information).

Note: If you want to actually run your application on your iPhone or iPad and submit it to the App Store, you need to join the official iOS Developer Program, which you can do right after you become a registered developer.

Xcode 4 is the latest iteration of Apple’s IDE, a complete toolset for building Mac OS X and iOS applications. With Xcode 4, you can develop applications that run on any iPhone, iPad, or iPod touch running iOS. You can also test your applications using the included iOS Simulator, which supports iOS 5 and iOS 6.

The Xcode IDE includes a powerful Source editor, a sophisticated graphical user interface editor, and many other features, including source code repository management. Moreover, as you code, Xcode can identify mistakes in both syntax and logic, and even suggest fixes.

Xcode includes everything you need to create your app — which is both the good news and the bad news. The good news is that it has everything you need. The bad news is that because it has everything you need, it can be pretty complex.