Welcome to my first guide. I'm new to LOL, just started playing it in S6. But i watched a lot of eSports and I'm a quick learner. This build will help you start playing LOL and you will enjoy it, because you will be able to beat a lot more experienced players. Garen was one of my first champs and in a few games I started regularry getting S grades and I even got a penta kill. I will try to improve this guide and I'm welcome to suggestions.

I will try to keep it short, because you didn't come to play LOL to read. Basically you try to do a combo Q (to silence opponent), E ( to do the damage, do at least 2 strikes to get Thunderlord), W (to reduce his damage). After that combo farm for a while, until you get Thunderlord back and than attack opponent again. When his life is low don't forget to ignite.

Your ultimate is very important as it can do a lot of damage. Key thing is to use his when your opponents life is low (less than a third of life). Never use is with more than half of life (only if you know you will die in 1 second). Usuallly use your ulti to end your combo. So press Q,E,(ignite),W, R (only when his life is low).

You are extremelly powerful level 3 and level 6, try to do most damage than. Against some champions you are even powerfull level 1 and 2, but be careful with the minions. Once you reach level 10 you should be able to push your opponent under the tower and then you can help other lanes, especially mid.

Q has some other uses too. You can use it too run (from base to minions), away from opponents. Also use Q when attacking the tower, you have no mana so you can use it a lot.

Also try getting first blood as you are really strong early. If you have low life just stay away from combat and you will regenerate a lot.

You have Q and E that will help you a lot with farming, but be careful not to overuse them. Especially try to save the Q is you get ganked by jungler, because the speed and silence can help you run away.
Once you have The Black Cleaver you will be able to farm all minions with only E.
If you are new to the game you will probably be bad a farming and with Garen you can hit minions a lot and you don't have to worry about last hitting a lot, but try to improve you farming skills fast. You can even train yourself to last hit with Garen.

As i said try to start helping team once you are around level 10 and more, you can help even before if you get early kills. Always go for the ADC and mid laner. They usually do most damage and you will just peel their life. Use your ulti on your villain (the one with a sword over his head) as you will deal him true damage, but don't use it if they have a lot of life. Don't forget to press W, which will protect you. Once your life is low it is smart to run away and go farming. You have a passiv regenerate which will help you get bakc to full life even without recalling.

So basically attack early, use Q,E,(ignite), W, R (when he is low life). Help your team when you get some items and you are around level 10. If you are low life step away from combat and regenerate. Use the right masteries with Thunderlord to get max damage early. Attakc squishy members of other teams.