This is my guide to how i like to play Olaf he is a very fun toon and once you get the hang of him hes virtually unstoppable. Hopefully this guide will help you get the hang of him whether you like to jungle or to lane i will post guides on both. If you like Ganking people this is the champ and guide for you!

PROS
Amazing jungle
Heavy hitter early and late game
Really good slow if used correctly
True damage on reckless swings can take down those toons others cant
And lets face it hes just plain cool

CONS
Squishy if you lane with him
If used wrong his slow will end you
Skill dependent toon (this is something i like about him but others might see it as a con)

Berserker Rage - For each 1% of health missing, Olaf's attack speed is increased by 1%.
This can be a HUGE life saver especially if you take alot of life steal and crit 8 hits and your back to full hp
Undertow -
Olaf throws an axe to a target location, dealing 50/90/130/170/210 (+) physical damage to units it passes through and slowing them by 24/28/32/36/40% for 2.5 seconds.

If Olaf picks up the axe, the ability's cooldown is reduced by 6 seconds.

Cost
55/60/65/70/75 Mana
Range
1000
This is both a blessing and a curse if you miss all your throws you will be doomed to die ALOT how ever if you land most of them you will get MANY MANY kills This is also a amazing escape mechanic toss it toward the champ who is chaseing you and you will most likely out run them also paired with his ultimate and ghost you cannot be stopped this skill also does a great amount of damage and should be used to harras as well as start and finish ganks

For 6 seconds, Olaf's attack damage is increased by 7/14/21/28/35 (+ [1% of maximum Health]) and he gains 9/12/15/18/21% lifesteal and spell vamp.

Cost
40/45/50/55/60 Mana
Range
700
THIS SKILL IS YOUR BREAD & BUTTER You should never be hitting something and not have this on this skill allows you to get your health up very fast also this is super important for jungleing with out this jungle Olaf would be almost impossible please upgrade this as soon as possible if your playing jungle!
Reckless Swing - Olaf deals 100/160/220/280/340 true damage to his target and inflicts 40/64/88/112/136 true damage to himself.

Cost
50/50/50/50/50 Mana
Range
325
This spell is quite amazing if you take alot of life steal you shouldn't even notice the damage to himself actually most of the time you wont notice this spell is a HUGE burst of damage on a short cool down this will dominate squishy toons like twitch and destroy tanks like shen or malphite i dont recommend useing this early game if your jungleing tho because if used in the jungle you could get a little low on hp and maybe run out of health potions or die however when going for a gank this is what you want to use.
Ragnarok-
Active: For 5/6.5/8 seconds, Olaf is immune to disables and reduces incoming damage by 20/30/40.

Passive: Olaf has 10/20/30 increased armor penetration.

Cost
100/75/50 Mana
Range
400
This skill is amazing pretty short cooldown conisdering what it does this is also your main escape mechanic pair this with ghost to ethier get away or chase also toss your axe toward the champion your running from or chaseing down also if you in a big team fight pop this to stay alive and to dish out a ton of damage!

ALWAYS USE Undertow to initiate and to finish ganks once you get into the fray turn on Vicious Strikes then just start beating the **** out of you them with Reckless Swing REMEMBER TO ALWAYS USE Undertow AND Vicious Strikes when there not on cooldown Use Ragnarok as needed say im super low hp and i need to get away but there team has a teemo who put shrooms in all the bushes well use Ragnarok and run for your life or there are 3 low to mid hp champs all in one lane and you think you can kill them well you prob can run in there throw Undertow at them turn on Vicious Strikes and Ragnarok then just use Reckless Swing and Undertow until they die.

while jungleing you may want to put down some wards here are the best spots to do thati highly recommend putting down wards sets up easy ganks lets you know when buffs are up and can give warning to your low hp teammates who are about to recall

OK lets get down to business when jungleing one think you have to decide is what route to take (what order to kill what creeps) i like to start at the golem camp but you can start at wolf camp or even the ghosts if you like i highly recommend starting at the golem camp tho since it provides much much more gold and experience here are some videos on what routes to take

This one is a very safe way to do it if your just starting out i recommend doing this route
http://www.xfire.com/video/400366/
If you have a good grip on how to play him and want to get some early ganks this is the route for you
http://www.xfire.com/video/40034f/

You should almost ALWAYS have the RED or BLUE buff its these buffs that make Olaf so deadly early game late game it is not as important but can still save you in a tough situation try to get these as much as possible.

Through out the course of the game you should be leveling off of ganks but in the event that you find yourself under leveled and in need of some quick experience go to a lane and kill some minions or if there are still creeps in the jungle farm them.