Is there a difference? Icloud unlock & factory unlock?

I've never had an iPhone, what's the difference in factory unlock & icloud? I've seen something about original owners, is it impossible for me to get an unlocked iPhone and simply make a new account and place a sim card inside?

A factory unlocked iPhone is one that is configured from the factory to be unlocked, as in work with any GSM carrier in the world.

iCloud is Apple's cloud based service. What I think you mean by original owners is Apple's new activation lock that was started when iOS 7 debuted where if the phone is lost or stolen & the person who found/stole it is trying to restore it to use as their own the phone would request the original owner's Apple ID & password, in effect shutting them out of it.

As far as getting an unlocked one & using it as your own, yes that is entirely possible. If new, simply a matter of buying it & setting it up (like I did with my last 2 iPhones). If used, ensure that the previous owner properly restored it to be sold so that the activation lock would not be an issue and just in case if it still does have their contact information available to help with the issue.