What is a .resx file

The .resx resource file format consists of XML entries, which specify objects and strings inside XML tags. This is useful for localization. For more details refer Resources in .resx files

How should I destroy my objects in ASP.Net?

ASP.Net actually has very solid internal garbage collection. So this is not an issue as it was in previous versions of Active Server Pages. Link to more information: <gcConcurrent> Element

Will the WebMatrix SqlDataSourceControl work with a MySQL connection

SqlDataSourceControl lets you connect and work with MS SQL DB, while AccessDataSourceControl do the same thing but for MS Access DB. Therefore SqlDataSourceControl can’t help you in your MySql connectivity . For Connectivity with MySql refer Accessing MySQL Database with ASP.NET

What is the difference between src and Code-Behind

Src attribute means you deploy the source code files and everything is compiled JIT (just-in-time) as needed. Many people prefer this since they don’t have to manually worry about compiling and messing with dlls — it just works. Of course, the source is now on the server, for anyone with access to the server — but not just anyone on the web. CodeBehind attribute doesn’t really ‘do’ anything, its just a helper for VS.NET to associate the code file with the aspx file. This is necessary since VS.NET automates the pre-compiling that is harder by hand, and therefore the Src attribute is also gone. Now there is only a dll to deploy, no source, so it is certainly better protected, although its always decompilable even then.