this picture just goes to show that leona is not only a great tank, but also a support. 2 for 1! she has a shield that at lvl 1 adds 30 armor and magic resist making her the best tank for early gank. (ive played against leona's who dont take it at lvl one and they ALWAYS die first). She has 2 stuns, one on hit and another long range AOE that stuns slows and does damage. this aoe stun can make or break a fight, while playing some 3's i would stun 2 or even 3 people at the same time and turn a loosing battle into 3 free kills. her zenith blade ability is really useful for ganks, and to get to pesky ranged damage in the back for an easy stun. As for building the recommended build has most everything you need, wich is CD reduction and lots of it. my normal build is Dorans shield> Boots> (ill get mercads here if they have an AP heavy team or alot of CC)> Kindlegem> Glacial shroud> Wardens mail> (if i dont get merc treads ill get ninja tabi here) >frozen heart> Randuins omen> and if you still haven't won trinity force is good.
Also disregard the loss, we had a bad game against a crit runed gangplank, theres really not much you can do about that.