An activity is a window that contains the user interface of the program. It can be considered a ‘page’ of the program, e.g. one activity might show a map with a gps location on it, and another activity might be a form to allow the user to input their location. In this example there are two activities in the application. An activity will have a life cycle, in a sense it’s born when the user calls it, and dies when it is no longer needed, and understanding this is important for application development.
An intent is the glue that binds activities together, and allows them to work with each other.