Google "How to run multiple diablo 3" and you get about 500 websites teaching you how to do it.
Type "Multiple diablo 3" into youtube and you get about 50 videos showing you how to do it.
Type "multiple diablo" or "multiple clients" into thebuddyforum search and you find at least 10 threads explaining it in three different methods.
So in response to your guessing - yes it was a retarded question that you didn't bother to research. I hope you learn to research now using simple terms and the internet that is at your finger tips.
<3 love love <3