Once you downloaded the ZIP archive, you just have to unpack it in some directory on your computer (or other hard-drive), make sure you have (at least) 150Mb of free space!
As this ist done, you just have to double-click on yPortableWS.exe (it should be the only file in the root of the yPortableWS directory) and a GUI should appear.
At this point you have to start the server applications (LightTD and/or MySQL) if you want to use PHP you need at least Lighty to run!
When the status "lights" are green you can test your setup's functionnality by accessing the intgrated portal at:http://localhost/portal/
There you'll find some information about the shipped software, aswell as access to the phpMyAdmin interface and to a litte benchmark!