The simple goal is to create a loop starting and ending with a gem by manipulating hexagons across a board. Each hexagon has part of a path on it - either a straight or curved stretch - and turning these allows you to create the objective loop.
It's not as easy as it sounds. Finding the right path, not to mention having to twist and turn all the hexagons so that they meet up, is actually quite difficult. Further complicating matters is the gem itself, which comes with its own piece of path, meaning it can only be linked up from certain angles. It's not uncommon to almost complete an entire loop only to get back to the gem to find it doesn't fit. That's because, at the start, there's no real way of telling whether the loop you're setting out on will work. Hexterity is very much a game of trial-and-error.