Create simple Plugin for Unity(Standalone and WebPlayer)

i want to create simple plugin for Unity3D. How can i create it? Which product i have to use(.Net OR Visual Studio)?

it generates .dll file and how can i open it?

thanks for reply but which product generates .DLL file?

Building a Plugin for Windows

Plugins on Windows are DLL files with exported functions. Practically any language or development environment that can create DLL files can be used to create plugins.

i saw it. Thanks