I have Ruby installed, but I still need to add it to the PATH variable. I found something online for how to manually add it using the command line:
set PATH=
Fear nothing, What you are doing is prepend C:\Ruby200-x64\bin to the existing %PATH%, this is what the command you posted does.
The path is a list of directories, separated by ;, in which the system will look for the command you execute.
In your case it's:
C:\Ruby200-x64\bin%PATH%, if you print it on the command line, you'll find it's itself a list of directories separated by ;.In case you want to make your change permanent, you have to change your PATH sytemwide.