Include the provided .a library into your Objective-C project. To do that in the Xcode, go to your project's Build Phases, press the + sign under the Link Binary With Libraries section, pick the Add Other... option nad navigate to the provided static .a library.

At the top of any source file where you want to use Enhance, you must include the library by adding the following imports (depending on which features you want to use):

#import "Enhance.h"
#import "EnhanceInAppPurchases.h"