May the Great Potato guide you...
This is my first guide and English isn't my native language, sorry for any mistake and grammatical errors. Hope you understand! :D
Volibear can be a hell of a tank, but he's a very nice support too, nobody can escape your Thundering Smash and you can combo it with the Sky Splitter for epic slows, this way you can give a lot of free kills to your ADC

You should MAX Thundering Smash first because it's your main support skill, right after, you should focus Sky Splitter for nice slow downs, combed with the Thundering Smash this skills becomes brutal.

Very nice skill combed with your Thundering Smash and Sky Splitter
It helps a lot the supporting!

You can throw anyone back with Thundering Smash, flash helps you escaping and closing gaps, but it can help a lot your Thundering Smash

The Relentless Storm Passive: When Volibear's health drops below 30% of his maximum health, he will heal for 30% of his maximum health over the next 6 seconds. This passive effect has a 120 second cooldown.
LOLOLOL
This will save you a lot of times, ignite almost cancel the effect of this skill, but at least you don't die :3
On Duels (x1) this is simply epic
LOLOLOL
Thundering Smash Active: For the next 4 seconds, Volibear will gain 15% movement speed. This bonus increases to 45% movement speed when headed toward a nearby visible enemy champion. Additionally, Volibear's next autoattack during this time will deal bonus physical damage and will fling the target behind him.
LOLOLOL
This is your main support skill, it can make anyone vulnerable to your teammates, especially the ADC, on the early game this will feed your ADC if used correctly.
You can combo this extremely good with Sky Splitter and Exhaust for a EXTREME SLOW
You can pursue very well with this skill.
LOLOLOL
Frenzy Passive: Volibear temporarily gains bonus attack speed after an autoattack. This bonus stacks up to 3 times and lasts for 4 seconds.
LOLOLOL
Active: While Volibear has 3 stacks of Frenzy, he can activate this ability to bite a target enemy. The stacks won't be consumed. The bite will deal physical damage that scales with his own bonus health. This damage will in turn be increased by 1% for every 1% of the target's missing health.
LOLOLOL
This skill rips the face of your enemies and kills them... until they are dead... today!
The passive is very good for destroying towers and killing creeps/minions, because it increases a lot of attack speed, with your Stormbringer it's a very brutal skill.
It's active bites the enemy and does a very good amount of damage, use this when the enemy is ~25% life, because it deals more damage for the amount of life your enemy has lost.
With this build you will have ~4500 health, Frenzy does 15% of your health as damage plus it's base damage (260 maxed)
LOLOLOL
Sky Splitter Active: Volibear lets out a powerful roar that deals magic damage and slows nearby enemies for 3 seconds. Minions, monsters and pets are feared for the duration as well.
LOLOLOL
You can slow down champions and fear minions and monsters with this epic roar you have, because you're a motherfu'''ing bear!
This will help a lot the Thundering Smash and the laning
LOLOLOL
Stormbringer Active: For the next 12 seconds, Volibear's autoattacks will blast his target with lightning that will also bounce to up to 3 nearby enemies. Each bolt of lightning will deal magic damage and will only hit each target once
LOLOLOL
Some think this ultimate isn't good, but on a TF it's extremely useful, and you can troll your enemies by attacking the minions and dealing damage at them without physical contact.

DON'T FARM
Help doing damage to the minions (usually the mages) for your ADC.
When many minions group you can use your Sky Splitter to advance the lane, because the minions will be feared and stop doing damage to your minions

Ninja Tabi it increases your defense and gives you 10% protection of basic attacks... but if you need magic resist ant tenacity you can buy the Mercury's Treads
LOLOLOL
Ruby Sightstone You're the support
LOLOLOL
Warmog's Armor Obviously huge amounts of health and good health regeneration
LOLOLOL
Frozen Mallet it will help slow down your enemies and give you health and attack, you need attack too
LOLOLOL
Atma's Impaler very good item for tanks, gives you armor and damage based on your health
LOLOLOL
Runic Bulwark gives you health, armor, magic resist and buffs your teammates, don't forget you're the support!

LOLOLOL

The Thundering Smash is your most epic skill, you throw your enemies in hell (aka ADC)
You can Gank very well thanks to the Thundering Smash, you can catch anyone them slow with Sky Splitter giving a free kill for the lane (usually mid) and helping destroying the tower, if possible.
LOLOLOL
At the Late Game the TFs are important, you are the main starter and can break their formation with the Thundering Smash, if you kill the target you will have an almost won TF, 5x4 is easy.
Use your Stormbringer at the start, it will damage many champions, giving your team health advantage.

Hope you guys liked it, tell me what's wrong and the grammar errors, give suggestions and help me improve this guide.
May the Great Potato guide you...