There is a rule sheet (next page), but you can start playing without it and refer to it as needed. Basically, three sets of pieces (the same sets as in conventional Chess) border each other on the outer two ranks of the round board. Since the "rows" are now concentric circles, a Rook may rotate around the entire board - [!!!!! -- the perfect Xmas upgrade] or move straight across the board passing through the center. There is no space to occupy in the center, you simply pass through it. By the nature of the board, diagonal moves "bend" toward and may rotate through the center. The "trajectory" lines on the board are only visual aids to help you see and plan possible diagonal moves. Diagonal moves such as a Bishop, may rotate through the center but cannot rotate through (or bounce off) the outer rank in one move. There are "Moats" between each team on the outer rank. They are necessary to keep Rooks from capturing each other on the first move. These Moats may become bridged if the outer rank between two teams becomes vacant. Also, there are Creeks that run two ranks toward the center off each Moat. The Creeks only purpose is that a Pawn cannot diagonally capture across the Creek (it must first be past the Creek).
Hat Tip MR. Ordering and more information here.