How do I make a p2p video streamer for Windows?

hi,
guess you will need:
a UI framework(MFC if target is only windows and language is VC++ (Microsoft's version of C++), otherwise Qt is a good cross-platform option)

For Windows, Microsoft Media Foundation now supports audio and video capture. you need to explore more and google for this.
you can start here:
https://msdn.microsoft.com/en-us/library/ee663260(v=vs.85).aspx
https://msdn.microsoft.com/en-us/library/dd758070(v=vs.85).aspx

streaming APIs are also there:
https://msdn.microsoft.com/en-us/library/hh828986(v=vs.85).aspx

maybe you can start by building a simple application which captures the input captured through the laptop camera. then add the functionalities one by one.

maybe this gives you some more ideas:
http://www.codeproject.com/Articles/1017223/CaptureManager-SDK