I don't have any experience using FuelPHP but have been using wordpress for a few years. I have a live website that was created using FuelPHP and I will need to start making edits on it. I don't want to make them on the live server, so I wanted to ask if someone could help me understand how to create a dev copy site and how to correctly edit and update files? Thanks.
A properly designed and configured Fuel application has no link to the hostname it runs under.
So you should be able to setup a different virtualhost, copy everything to it (make sure the documentroot points to the directory the index.php is in, by default /public), make a copy of the database to your test server, and make sure the db.php in fuel/app/config/development points to that database.
After this, it should run file. If not, you'll have to start debugging because the person creating it did something non-standard.