Brand. In this tank meta, his passive, 8% health Dot is great for dealing lots of damage with little items. Combine this with his Q stun, great team fighting with his R, wave clear with his W, and you sir have a support that can fight back.
One of the best ways to get better as a new player is to learn every champions abilities and general Cool downs. If you know what your opponent can bring to the table you will be able to play to their weaknesses. 
Weakness are that he is immobile and his ultimate can be tricky to use. Also his Stun is situational as you need the target to be ablaze first and you have to land the skill shot.