Set up a staging site?

Hello,
Just learned from Nastia in this thread https://premium.wpmudev.org/forums/topic/untangling-loginregistration-issues-for-my-membership-site#post-1203285 that my first step for transitioning my mulit-site membership blog from s2member to Membership 2 Pro would be to setup a staging site. I need to accomplish this as quickly as possible (the transition) and would appreciate as much help as I can get. Is there someone available to help me with this? I've found no easy answers here about even this first step and feel I could spend hours just trying to find out how to create a staging site.

Would love to give my credentials and get as much assistance as possible!