A good staging server plugin that is SIMPLE?

Forgive me if I’m being stupid, I’m not much of a web dev guy, I’m more of an interface designer. I make WP sites for friends, and I do not make any money off them.

I want to create a staging location for my WordPress installation. A place where I can make changes and experiment before taking my changes live. I’d like to have an environment where I can mess around with the site and add/remove content, pages, and styles without pushing the changes to the live site. Then, when I get it just right, I can push it live with a button click.

Is this an option?

I know I could just create a subdirectory and have a second wordpress install located there, but I don’t know of a way to push changes that I make there to the main site in an easy way.

PHP/SQL confuses me a LOT. I’m very much a GUI person and not a command-line person.

Thanks in advance, I appreciate all constructive responses. ??