There's no official ruling, no.
I can say it's not like The One at all, where people are basically rendered down into streams of particles to be squirted through a black hole, nor is it like Terminator, which was time travel and not a point-to-point teleport.
It can probably best be described as stepping into a well of energy and suddenly being somewhere else. There's probably some brief disorientation, less so the more one does it. It's a quick trip, though not necessarily instantaneous. I would guess there's a brief sensation of the transit, maybe even some small sense of velocity, but it wouldn't be anything like the wormholes on Sliders or Stargate (pick one).
It's probably most like Star Trek, only faster...but then, these are all technological systems. Portals are magic. You step in, are surrounded by magic and then you're somewhere else.