Difference between .asmx, .aspx and .ashx

a webpage provides a graphical user interface (text, images, buttons, etc.) while a web service does not provide a graphical user interface. It is mainly used to fetch data and perform actions.
aspx = page in WebForms. Contains controls and events
asmx = web services. Modality of sharing information from/to website
ashx = generic handler. Can be used in various ways* as generate pages, sharing information, display pictures...
. asax : Global.asax, used for application-level logic
.ascx : Web UserControls: custom controls to be placed onto web pages.
.axd : when enabled in web.config requesting trace.axd outputs application-level tracing. Also used for the special webresource.axd handler which allows control/component developers to package a component/control complete with images, script, css etc. for deployment in a single file (an 'assembly')
. config : web.config is the only file in a specific Web application to use this extension by default (machine.config similarly affects the entire Web server and all applications on it), however ASP.NET provides facilities to create and consume other config files. These are stored in XML format.
.cs/vb : Code files (cs indicates C#, vb indicates Visual Basic). Code behind files (see above) predominantly have the extension ".aspx.cs" or ".aspx.vb" for the two most common languages. Other code files (often containing common "library" classes) can also exist in the web folders with the cs/vb extension. In ASP.NET 2 these should be placed inside the App_Code folder where they are dynamically compiled and available to the whole application.
.dbml : LINQ to SQL data classes file
.master : 2.0 master page file
.resx : resource files for internationalization and localization. Resource files can be global (e.g. messages) or "local" which means specific for a single aspx or ascx file.
.sitemap : sitemap configuration files. Default file name is web.sitemap
.skin : theme skin files.
.svc : Windows Communication Foundation service file