Using Windows 8.1 from external hard drive

I was told that i could test Windows 8.1 by installing it to an external hard drive and running it through my PC. I tried using a program called Win2USB or something like that. I had created a new partition and managed to copy the files from the Windows 8.1 disk to the partition, the copy i presumed was bootable. So what would i do now? I am running Windows 7 and want to plug in the external and have it boot up Windows 8.1 as i start up my PC. Thanks.

WinToUSB > WinToUSB - Install & Run Windows/WinPE on a USB drive!

Does all the work for you - you do not need to copy any files over to the USB manually...
So your usage of the program may be flawed.. You could use a 16GB USB, but a 32GB is better...

Not knowing your partition selection and setup process, it is hard to say, but with the USB plugged into the PC you would then have to bring up your BootMenu (usually F12) and select the USB as your Boot Device..
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There is another program (that I use) to do the same thing WinToUSB does, But this program does it better and offers more options..

WinNTsetup > http://www.winntsetup.com/