Thanks for the responses.
My model is a Samsung Galaxy S4 on Virgin Mobile (carrier).
I have put in SuperSU and it seems to open fine without giving me any errors, but looks quite empty in general.
I'm going to try that link you posted now, it seems to be specific to my device.
The guide I used can be viewed here:
Root I337MVLUAMG1 Samsung Galaxy S4 SGH-i337M 4.2.2 Update - Androidayos