The concept is fairly straightforward. Each side has their own portal, which they can move one step in any direction. Going through a portal means your piece's particular style of movement continues through your opponent's portal. There are a couple of other details and rules, so you should watch the full video for them.
Definitely going to try playing this one with my dad. Since, you know, I beat him that one time. And I may very well do so again.
How to play Portal Chess! [YouTube via Reddit]
