Projects can become quite advanced in Visual Basic, even containing sub-projects of different types. From a programming point of view, however, standard Visual Basic projects usually contain just three types of items: global items, forms, and modules.
Forms: They are the templates you base windows on. Besides standard forms, Visual Basic also supports Multiple Document Interface (MDI) forms, as well as a whole number of predefined forms.
Modules: Modules are collections of code and data that function something like objects in OOP, but without defining OOP characteristics like inheritance, polymorphism. The point behind modules is to enclose procedures and data in a way the hides them from rest of the program. This is very important for maintenance of the program.
Global Items: Global items are accessible to all modules and forms in a project, and you declare them with the Public keyword. These items should be minimum in the program. These should be only used to exchange the data between forms.