the "Variable name" is "PATH". It should already exist in your system, and you should edit it and append to it, separated by a semicolon, the location of the visual studio's c++ compiler cl.exe (which in your case seems to be "C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC", but you'd better double check that).
Make sure you reboot once you change the PATH variable.
Make sure you reboot once you change the PATH variable.