Through playing support main I have found that there are a lot of great champs for different team and players. Leona's damage, range, strength, and CC makes her extremely strong early game along with dynamic with a good ADC and a beast late game. I hope you find as much success with her as I have along with endless fun!
The support role is, to me, the position that really determines if a team will win or lose. They help feed your ADC early game, give vision of the map (hopefully with a little help from your jungle and position players), and heal, stun, or protect your fellow team mates.
I pride myself on being a leader in the game and directing my team so that others can focus on CS and total domination. In my opinion, every support should be able to do this. GL HF.