WPI is short form for Web Platform Installer.Those already using webmatrix will be knowing it that the webmatrix is installed from the Microsoft Web Platform Installer 4.0 and if you have already installed the RC version of webmatrix before then you will have this already on your machine.Just search for it in your installed programs and you will find it —
In the WPI you will see WebMatrix 2(highlighted above) just click Add and then Install
click on I Accept
wait for the installation to finish
click on finish to complete the installation and you are ready to use it
If you are new to this then go WebMatrix site and click on “free download” you will have a program downloaded named webmatrix (icon shown below)
Double-Click on the icon to start it and you will have your WPI installed after which you will be guided by the WPI to install WebMatrix which will be similar to the steps shown above.