The Android SDK includes a mobile device emulator — a virtual mobile device that runs on your computer. The emulator lets you prototype, develop, and test Android applications without using a physical device.
The Android emulator mimics all of the typical hardware and software features of a typical mobile device, except that it can not receive or place actual phone calls. It provides a variety of navigation and control keys, which you can “press” using your mouse or keyboard to generate events for your application. It also provides a screen in which your application is displayed, together with any other Android applications running.