Have installed Visual Studio 2012 Trial, but it doesn't add any icons to the desktop.
So how can I open it and then add the icons to the desktop in Windows 8?
Assuming by 'Trial', you mean the Visual Studio Express version, go to the start screen, and type 'VS'. You should see a 'VS Express' show up in the search results for applications.
Win + Q opens the search menu, type here "visual " and you should see an icon of VS 2012 - start it. During the program runs you can always add the icon to task bar or whatever ...
I do not has installed MSVC 2012 but have MSVC 2010. I think 2012 has analogue path to start application :
%Program Files%\Microsoft Visual Studio 10.0\Common7\IDE\devenv.exe