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).