Acticity :Activity represents a single screen in yout app with which your user can perform a single, focused task such as taking a photo, sending an email, or viewing a map. An activity is usually presented to the user as a full-screen window.
MainActivity.java : which is presented to the user when the app is launched. The main activity can then start other activities to perform different actions
View ：The View class represents the basic building block for all UI components, and the base class for classes that provide interactive UI components such as buttons, checkboxes, and text entry fields
Intent : An Intent is an asynchronous message that you can use in your activity to request an action from another activity, or from some other app component. You use an intent to start one activity from another activity, and to pass data between activities
Bundle : A Bundle is a collection of data, stored as key/value pairs.
eg: To pass information from one activity to another, you put keys and values into the intent extra Bundle from the sending activity, and then get them back out again in the receiving activity.