iPhone StoreKit implementation problem

I am trying to add the iTunes storeKit and am somewhat unfamiliar with Xcode.
I found this tutorial http://troybrant.net/blog/2010/01/in-app-purchases-a-full-walkthrough/ . At #7 of the first section is the storekit code samples.
What I am having a problem with is locating the files in Xcode itself and once I have, how do I fetch this information that has been added in Xcode and get my GUI to call it up?

for eg.
Finding the .h and .m files?
Do I place the fetch in my GUI touch in out?
And What do I write to fetch the xcode information?

function Update()
{
for (var touch : Touch in Input.touches)
{
if (guiTexture.HitTest (touch.position))
{
Get StoreKit item - “ProUpgrade”
}
}
}

Please don’t say Prime31… And if Prime31 how much am I going to struggle getting that to work?
Thanks, any input or suggestions welcome…

And once the purchase is made, I want a value in my game to show 1. Does the iPad store the purchase information if the game gets unistalled and installed again?

We offer a FREE native plugin that provides in-app purchases with Apple hosted downloads, and an easy to use API. It also mirrors the exact native StoreKit framework with 20 classes and 102 methods if you want to use advanced functionalities and customize implementation. There are examples, tutorials, and videos showing you how to use it.

Asset store link of the free U3DXT Basic: https://www.assetstore.unity3d.com/#/content/11817

We also offer a Pro edition that comes with GameKit, Social Networking, Face Detection, iOS 7, Speech, Game Controllers, Multipeer Connectivity, Media Player, AddressBook, EventKit, and much more to come. https://www.assetstore.unity3d.com/#/content/9555