c# - How to import or "using" a custom class in Unity script?

I have downloaded the JSONObject plugin for parsing JSON in Unity but when I use it in a script I get an error indicating JSONObject cannot be found. My question is how do I use a custom object class defined inside another class. I know I need a using directive to solve this but I am not sure of the path to these custom objects I have imported. They are in the root project folder inside JSONObject folder and class is called JSONObject.

Thanks