I am following a tutorial which introduced the global JSON object to stringify objects, in the tutorial they mention that this JSON object and it's methods is provided by the browser. I've also looked at the MDN page for JSON and they list it as a standard built in object.
I'm trying to understand if an object such as this is the same as the Date or Math objects and is built into Javascript or is it something extra that is provided by browsers implementing it?
Yes, it's a built-in object that's a property of the global object, as the specification requires for implementations of ECMAScript - just like Date and Math and many others.
Generally, if you want to find whether a particular object or method is universal, see if the ES specification or DOM standard says anything about it. (That said, just because something's in the standard doesn't mean that it'll be implemented everywhere - even some modern environments are not spec-compliant in a number of areas.)