There are many type of extensions in asp.net 2.0. Brief introduction is given below:

asax : This extension is of Global file.

ascx : User controls having this extencion.

asmx : Web services pages

config : This is extension of web config file.

cs/vb : These are code files extensions. We also called them code behind files.

master : This is extension of master page.

resx : resx files are useful in globalization or localization.

sitemap : These files are used in sitemap controls.

skin : These files used when we used themes and skins.