There is a thread up top labelled noobs guide to flashing. It has the stock rom link available.
You will need to run Odin before next step.
You will put the phone into download mode.
Do this by holding down the power up and power down button as you plug in the usb cable.
Your phone should recognize ODIN.
Follow the steps in the Noobs guide to flashing on how to load the files into ODIN.
It is very simple because you dont change any settings in ODIN. You leave it how it is and it really makes flashing back to stock pretty easy
Let me know if you have any questions.