Hi i am creating visualforce pages and apex classes triggers etc for last some time.i want to know what is app in salesforce and how to publish it on AppExchange? Any requirement for publishing app on app exchange i went through this tutorial link
they teach how to create an app in developer org by default there are 6 tabs Home,Chatter,File,Your Tab ,Reports,DashBoard.i basically want to know what app contains? apex class,visualforce page these components or only standard tabs and some customization tab what we see when we select an app in developer org