ColbyCheeZe presents a very nice guide on Leona, the Radiant Dawn. Leona is quite a unique champion because of her multiple stuns and area damage which makes her a great initiator. Furthermore, Leona’s Eclipse provides a fair amount of resistances to effectively act as a tank.
ColbyCheeZe’s guide provides examples of how to play Leona as support in a duo lane. Additionally, it clearly shows how to perform her combo and when to use it. Finally, you can also find advice on Summoner spell choices, masteries, runes and a suggested item build.