Yeah, I'm completely new. I just learned on youTube how to root. Apparently I first have to unlock the bootloader. What is SOFF and GPE? Sorry for the newness here.
GPE = Google Play Edition; it's the version of the One that you can buy direct from the Google Play Store, and it uses stock Android software as opposed to HTC's Sense software.
S-OFF is a weird thing. HTC handles their firmware/software a bit differently; when you get the device (stock) it's shipped S-ON, meaning that you cannot "write" to a certain partition of the software (the NAND, if I recall correctly). In order to gain
full control over the device, not only must you unlock and root the device, but you must achieve S-OFF so you can "write" to that partition. For example (IIRC), one cannot change the bootloader ("HBOOT") on an HTC device, in particular the One, without achieving S-OFF. In the ye old days of HTC, the only way to achieve S-OFF for some devices was to physically change something, I believe it was a matter of touching a wire to something else (I didn't have one of these devices, so pardon my ignorance). With the One, you can achieve S-OFF through certain pieces of software and loopholes. When I achieved S-OFF, it required a variety of different steps because an AT&T update closed the previous loophole. Now, I believe the process is much simpler and has been reduced to piece of software, but you may want to read up as I sold my device months ago.
I needed S-OFF for two things: to reset any sort of "tampered" flags from unlocking the bootloader and to be able to install the complete GPE firmware, including the GPE HBOOT/bootloader. Otherwise, you can flash (install) a GPE ROM. The benefits of a full conversion is that all of the software is stock and it is updated very quickly through Google/HTC, as opposed to being at the mercy of the carrier. I also had to change the CID (cell ID, if I recall correctly) so the GPE firmware/software would properly install.
While hacking the One is a lot more straightforward than most devices, it's not even close to Nexus devices. I recommend reading up on it a bit, watching YouTube videos, and asking questions if you are unclear.
Good luck.