OK, you're on Jelly Bean. Without rooting, there is no way to use WiFi for tethering. Sprint "fixed" that loophole. Rooting this phone is easy if you're careful about following instructions. If you want to do that, read the first post in this thread:
http://forums.androidcentral.com/sp...e-updated-how-root-your-sprint-galaxy-s3.html . Then read it again. Then read the whole thread. If you have any questions, ask before you start rooting.
If you don't want to root, there are a number of apps in the Play Store that provide USB tethering. I don't know if anyone has tried them with this phone on JB or not, but there are plenty of free ones, so give it a try and let us know.