INTRODUCTION
Gragas is a late AP champion he has very interesting spells that can target multiple enemies.He's 1st spell called Barrel Roll he throws a barrel that explodes and deals damage it can target even 5 enemies its a very good spell because it has very long range and plus you can steal kills.So enough of the spells i will tell you more about how to farm with Gragas
FARMING
So with the farming it will be very easy you will need to try to get your Rabadon's Deathcap and than you will just throw Barrel Roll but before Rabadon's Deathcap you will farm in a combo you will throw Barrel Roll and than at the same direction you will cast Body Slam its a very nice combo to kill minions.So try not to miss a lot with the Barrel Roll and try to get them with the Body slam.Always i repeat always use your Drunken Rage it regenerates your mana and its no cost a very good spell.Now i will teach you Team Work
TEAM WORK
Gragas is a very good team player because in a team fight he has 3 spells that target multiple enemies and that is very good and plus his spells can kill one versus one its excellent for team fights i recommend you to start with the Explosive Cask it damages all enemies and it pushes them to your team its very strong.Also just to let you know you can use Explosive Cask in your lane when you become level 6 because you will push them to your turrets and because they will be level 6 they wont have enough Health to survive.No i will teach you why do you need this summoner spells Flash and Ignite.
Summoner Spells
So the Summoner spells Flash and Ignite are played on many champions mostly on mage so they will do good because Flash 1st its the most useful spell in the game you can run from enemies like that or you can chase enemies like that and also its a very good combo you use your Body slam and than you use Flash its like dabble escape or dabble chase but if you run use Body Slam first than use Flash and if you chase use Flash first and than Body Slam but make sure you don't make a fail with Flash or Body Slam.For Ignite now use it its very good for early game for killing enemies on low Health.Try to get first blood with Gragas it will be very easy for you and plus with the ignite it will be easy.
RANKED PLAY
Gragas is a hard champion in ranked games i have to say because you will have to play him solo top or mid i never played him in ranked but i played him mid and solo top in normal games.For solo top and mid they are other guides i will recommend later.I played Gragas with a lot of other champions and i will recommend for you partner in lane need to be someone with range spells like Lux and Nidalee but i thin they are also some other champions like Mordekaiser or Yorick someone that can be a very good pusher.Now i will tell you about the Jungling and Creeping.
Creeping/Jungling
So with the creeps.You will target the range minions you will kill them with Barrel Roll very easy after you make Rabadonn's Deathcap so before that you will make the combo that i think i sad it before but i will say it again you will use your Barrel Roll and than the Body Slam.Its a very nice combo that you will use.Now i will tell you another tip about how to make your creeping easy.So you need to use Drunken Rage not only to regenerate your mana you will need to use it also for the extra damage you get and kill the minions on low health.
For the Jungle you wont need it a lot you will just take the blue buff more often because in
late games your Drunken Rage wont help you that much because you will need to cast your spells more faster and to don't care about your mana that much because it you will use a lot of spells in team fights or when you are ganking and it will be a lot of pain to use your Drunken Rage all the time.

PROS
1.You have a very good minion crowd control with Barrel Roll and Body Slam.
2.You have a passive spell that heals you for every spell you use(Happy Hour).
3.You have a spell that regenerates your mana and its no cost for that spell(Drunken Rage).
4.You have a spells that target all enemies and make a lot of damage.
5.You have a spell that gives you attack damage and lets you farm a lot better with out mana(Drunken Rage).

CRONS
1.You have a spell when you cast it you can't move(Drunken Rage).
2.You have a spell that you need to press 2times to be active(Barrel Roll).
3.You have a ulti that can help you or your enemies(Explosive Cask).

So as you see you have more Pros than Cons and that's good for you and plus about all the Cons except the 1st because the other two you just need to learn to time them right.


SPELLS

HAPPY HOUR
Gragas takes a drink form his cask every time he uses an ability,restoring 2% oh his maximum health over 4 seconds.

BARREL ROLL
Graggas rolls his cask to a target location,which can be activated again to explode after arriving or will explode after arriving or will explode on its own after 5 seconds,dealing 85/135/185/235/285(+90% of ability power)damage and slowing the attack speed of enemies struck by 20/25/30/35/40% for 3 seconds.

DRUNKEN RAGE
Gragas guzzles down brew from his cask,channeling for 1 second.He gains 30/45/60/75/90 mana while channeling,and becomes empowered after finishing,increasing his attack damage by 30/40/50/70/,and reducing damage taken by 10/12/14/16/18% for 20 seconds.

BODY SLAM
Gragas charges forward,colliding with the first enemy unit he hits and dealing 80/120/160/200/240(+50% of ability power)(plus 0.66 per attack damage) to enemies in the area.Damage is split amongst targets hit,minimum 50/75/100/125/150 damage.Units hit by Body Slam are slowed by 35% for 2.5 seconds.

EXPLOSIVE CASK
Gragas throws his cask to a location which explodes on impact,dealing 200/325/450(+100% of ability power)magic damage to all units stuck,knocking them back.



How to play him in Early game Mid game and Late game
Early Game
So Gragas is not that much of a early game player you need to know you will play him more defensibly and you will try not to get in a close combat fight expect if the enemy champion is not on low health.You will push the lane with your Barrel Roll and Body Slam you will kill a lot of minions like that and you will push the enemies back to there turrets.If they are some champions better lane you will try to play at the your turret so if they go and attack your turret you will just cast Barrel Roll and push them back.If someone attacks you in close combat you can kill him if he is not doing a lot of damage because you will not miss with your spells even once.
Mid Game
So the mid game it will be very easy to kill minions because with one Barrel Roll you will a whole troop of minions.But just for doing that you will need at list to have Rabadon's Deathcap.The minions that are range you will kill them easier than the close combat minions so sometimes you will have to cast Barrel Roll and than Body Slam.In mid game you will start the team fights so try not to just stay there and steal the kills use all your spells in the team fight at the beginning because even if you have some assists it will be steal good because you will need to have the items in late game.
Late Game
So late game is a very hard time for all the champions everyone has kills and nice items.So you will not play him that much defensively but steal don'g go 1vs3 or more.In late game they are some champions that you can't kill so always target the squishy once they die really fast with your combo of spells.You have some champions like Tryndamere that you cant kill even if they are squishy.You have a problem with Gragas because he has a lot of health but he still dies fast so that's the biggest problem in late game even if you have a lot of health you will steal need to go with your range spells.

Items you will need to have on Early Game Mid Game and Late Game
Early Game Items
3Doran's Ring and Sorcerer's shoes
Mid Game Items
Rabadon's Deathcap and Lich Bane and try to have at list Blasting Wand for Void Staff
Late Game Items
Void Staff Ryle's Crystal Scepter and Zhonya's Hourgalss

When to buy the items
So you first start with Doran's Ring than you will stay in lane and you will go back to lane when you have to buy 2Doran's Ring and Boots of Speed.Than you will go back to lane or start ganking try to get some kills and when you go back to base you will buy Sorcerer's Shoes and Blasting Wand or Needlessly Large Rod.Than you go ganking or team fights and when you go back buy Rabadon's Deathcap and Sheen than go back killing and than buy Lich Bane and try to have the money for Blasting Wand.So in late game you will buy Void Staff and for Ryle's Crystal Scepter you will buy first Giant Belt and Blasting Wand then you team fights and you buy the whole item and for the last item you buy Needlessly Large Rod and than Zhonya's Hourgass.

So they are different ways to play Gragas more faster ways to play him if you have a lot of money of killing.
So instead of buying 3Doran's Ring buy the Rabadon's Deathcap in early game.
If you like to play Gragas more tnaky than you will make Mercury's Treads Rod of Ages Ryle's Crystal Scepter Banshee's Veil Abyssal Scepter and Frozen Hearth.
Also you can play gragas with mejai's soulstealer.
The 2 build on gragas is more tanky at the beginning and you play him like this solo top.And with the first build you play gragas mid or with a lane partner.The 3 build is just for mid and its rly tanky so the 1 build in lane with partner with the 2 build solo top and with the 3 build you go mid.