The two arrows in the schematic pictures indicate the two sides about which the two stacked tiles are allowed to hinge. For example, the configuration I-1 (click on the I1-I3 image below) can be directly opened to obtain the starting configuration RRRURRRU or the ring shape RRmRRmRRmRRm, whereas the configuration I-3 can be opened into RmRvRmLvRmRvRmLv (and also into the starting 2x4 configuration).