A target is a collection of parts along with rules and settings for how to build a product from them. It is a major determinant of how an app is built. Whenever you build, what you’re really building is a target.
Select the Empty Window project in the Project navigator, and you’ll see two things on the left side of the editor: the project itself, and a list of your targets. In this case, there is only one target, called Empty Window (just like the project itself). But there could be more than one target, under certain circumstances. For example, you might want to write an app that can be built as an iPhone app or as an iPad app — two different apps that share a lot of the same code. So you might want one project containing two targets.
If you select the project in the left side of the editor, you edit the project. If you select the target in the left side of the editor, you edit the target. I’ll use those expressions a lot in later instructions.
Edit the target and click Build Phases at the top of the editor (Figure 6-9). These are the stages by which your app is built. By default, there are three of them with content — Compile Sources, Link Binary With Libraries, and Copy Bundle Resources — and those are the only stages you’ll usually need, though you can add others. The build phases are both a report to you on how the target will be built and a set of instructions to Xcode on how to build the target; if you change the build phases, you change the build process. ...