1. every module must have exactly 1 view control. In the module's definition this is the control that does not require a key (querystring paramater) to be loaded. The edit control is not needed, but is used to allow for an interface to edit the content of the module. If you look at the Text/HTML module, this is an example of a simple module with a view control, an edit control and a settings control (which is loaded in the module settings of the module)
2. there are 2 different development methods: Web Site Project (WSP) and Web Application Project (WAP). WSP used the app_code folder to put code for the module that is not tied to a user control (.ascx). WSP modules are not compiled and will be compiled during first use of the module. WAP modules are fully compiled modules (all code goes into the DLL of the module), and subsequently don't need the app_code folder. For more info on the difference between the 2 see Mitchell Sellers blogpost : http://www.mitchelsellers.com/blogs/articletype/articleview/articleid/171/wap-or-wsp-which-to-use-and-why.aspx

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