pretty sure there's a shell guide in archives...just search forum.
crit chance increases the chance of a critical hit by 7%
7% more damage to monsters of type "low level society" - this includes rebs and most monsters you "mob" for woa/5.2 leveling
light prop - this adds light element to your attack (doesn't really enhance damage outside of light sps since they have light property in skills)
sl damage/overall/etc. - adds sl points to the stat stated (this is one actually + NOT 1 POINT IN SP CALC). ie. if your sp is 80/0/0/0 the shell makes it 98/0/0/0/. you also get the bonus effects at +90 in atk (EFFECTS FOR +90 DO NOT SHOW UP ON YOUR SP BUT THEY WORK).
cxp = job exp as stated above
% dmg in pvp - self explanatory (this applies in fc as well)
reduce shadow res - reduces dark res by % shown