An application is a program, that allows a user to communicate with devices using screen buttons, switchers, charts, text columns, audio signals, and so on. More about this in the Creators Studio Guide.
When you press Add new application on the station's info page you are shown the following tab.
Create new application. You can create your own application in the Creator Studio.
Choose from Existing applications. You can add an application among those you have already created.
Buy on Marketplace. You can buy an application that has been already created.
Request. You can request the development of a customized application.