Swift is a multi-paradigm programming language created by Apple for developing iOS, OS X, and other Apple apps. The document discusses Xcode, the integrated development environment for building apps with Swift, and provides examples of building iOS apps including a postbox location app and music quiz app. It highlights challenges faced like accuracy of user coordinates, parsing JSON data, and using interface builder constraints, and solutions like using MapKit, CoreLocation, web APIs, and libraries like SwiftyJSON.