[Verizon Samsung Galaxy S 4] pstgh:
Sounds like you've not been successful in flashing the nc5. You're right about not being able to successfully install safestrap until you have root access- so, let's not worry about that for now. You've downloaded both of those kernals (Nc5 and Nk1) and have them on your pc, right? You have towelroot.apk installed on your phone, right? Which version of Odin are you running on your pc when you try to install / flash those kernals? The method is to plug your phone into the pc (via usb), turn it off (after making sure it is connected - you may need certain drivers on your pc for it to connect, but I believe those will get installed automatically when your phone is on in regular mode and you connect it to the pc). Also, remember to make sure that you've turned on developer usb debugging on your phone- that's been done, right? Assuming answers to all of these questions are yes, go ahead now and turn your phone off. Now (or later, it doesn't really matter), fire up Odin on your pc. Now, with your phone connected, power up your phone in that programming mode (can't recall what the official term is) by pressing and holding all three of the down volume button, the home button, and then the power button. Once you feel it buzz / bump, let go of everything and it should boot up into programming mode. Now put it down and from within Odin, make sure those two default boxes on the left middle are checked, then select the nc5 kernel by clicking that button on the right- depending on which Odin you have, it will be different (after 3.09 I believe they changed it to read AP). I'm trying to write all of this by recall, so if you don't understand what I'm saying- go back and review people's description of how to work Odin, but once you do that properly, you should see it flash that kernel and then there will be a green box on the top left of the Odin screen and it should say "Pass". That's how you know it worked properly. Now, reboot your phone and it will / should act very wonky, but hopefully, eventually, you can run towelroot and get root. Once that is completed, just turn the phone off and then reboot it into programmer mode again and, using Odin, flash the NK1 kernel. Seeing "Pass" again when you are done. Reboot again and you'll be all set with rooted NK1. Now install Safestrap 3.75 onto your phone. Make sure it's that version. Go into Safestrap and click "install" - not sure why, but just installing the app doesn't actually run the recovery part of Safestrap until you click install and see it report back that, with root access, it has installed successfully. Now, when you reboot your phone into that programming mode, it will bring up Safestrap. From there, you install that zip which will unlock your wifi tether (assuming that is something you want to do).

Hopefully this helped- let me know where you were falling off the trail here and I'll help if you're still getting stuck.

Just went and checked my Odin- I used Odin 3.10 and the options "Auto Reboot" and "F. Reset Time" both need to be checked. Then, click the little box on the left of the large "AP" button. Then click the "AP" button, find the kernel that you are flashing (from your pc), and finally click "start".