"iOS Simulator allows you to rapidly prototype and test builds of your app during the development process. Installed as part of the Xcode tools along with the iOS SDK, iOS Simulator runs on your Mac and behaves like a standard Mac app while simulating an iPhone, iPad, or Apple Watch environment. Think of the simulator as a preliminary testing tool to use before testing your app on an actual device.
iOS Simulator enables you to simulate different iOS and Apple Watch devices and several versions of the iOS operating system. Each combination of a simulated device and software version is considered its own simulation environment, independent of the others, with its own settings and files. These settings and files exist on every device you test within a simulation environment."