Olaf is a great DPS Champion.He can deal great damage just from his spells and Attacks and also chase down enemy champions easy.

On an uncharted continent beyond Valoran's grasping clutches, the conqueror named Olaf was born to a long tradition of soldiers unlike most others. Berserkers, as they tout themselves, are warriors who channel fury deep from their cores, unleashing pure and savage wrath upon their enemies. This fearsome evolution is a product of their unforgiving home, Lokfar - a barren tundra where all creatures must vie bitterly for every resource. Olaf belonged to a seafaring clan known for ruthlessly pillaging any and all villages within reach of their dragon-crested longboats. The last time he saw his icy home, Olaf was embarking on an expedition to pioneer and plunder a distant land known only to legend. However, while underway, a terrible storm sprung up and Olaf and his crew were thrown to the mercy of a roiling and pitiless sea.

His ship destroyed, his crew nowhere to be found, Olaf miraculously washed up untold miles from "friendly" waters on the foreign shores of Valoran, south of Demacia. This unfamiliar place stunned and frightened the Berserker, for Lokfar is not privy to such potent magicians. Approaching them, Olaf hoped that they could use their mysterious powers to send him back to his people. A bargain was struck. Olaf would use his awesome prowess as a warrior to serve the unusual wars of Valoran in the League of Legends, and in exchange the sorcerers would find him a way to return. Despite his participation in the League, Olaf knows better than to trust the "finger wagglers" that run the Institute of War. He deliberately keeps details of his life and home from them. After all, with enough information, they would most certainly find the Lokfarians and dominate them as they have dominated all of Valoran, keeping both quietly -- and unwittingly -- in their thrall.

Beware the war cry of the Berserker. What surges toward you is unyielding, free from the shackles of reason.

I pick Armor Pen. flat armor and magic restist.The reason why i dont pick Flat health is that i want to get his passive's bonus easier but for someone who want to play olaf as a tank its a great pick also magic resist/lvl is a great rune set but it will "block" your passive a litle bit,From the other side Armor Pen. runes are the best pick and also bonus his ultimate's passive

I try to Olaf offensive.I pick all offensive masteries on Offence tree and i pick the health and mana regen masteries on Utility Tree and I also pick the exp bonus to level up my spells faster

I start with and then as soon as possible i buy and turn them to then i buy but u can also buy insteed,I allways want to buy and then a .Ussually the game will end this far but if its not get a , and a .I have to say that u can buy the items in which order you like and fits you :D

Pros

Great damage dealer on early game
Usefull Ultimate for team fight or escapes
Great chaser
excelent control on solo lane


Cons

His deals true damage to an enemy so take care when you will use
Not so good jungler ( cant gang easy )
He lose easy mana on early game
He cant take on evry team fight his team

Try to max his E and then W,i end with maxing Q last.The reason that i max his E first is the true damage deal on both he and his enemy ( which gives his a "start" for my passive) and also allow me to secure my kills easier. the W gives you a great amount of lifesteal and spell vamp which work with his allready maxed E.