My first week into League of Legends and I have a few questions!

I go into League a week ago & my friend suggested that I start with Garen who is the best to give you a feel of the game without complicating things. I started using Garen & Sona a lot but Garen is my first pick almost every game.​I just had a few questions on how to properly utilize Garen. I really enjoy taking on fights or 1v1s and chasing enemies if they are low. MOST of the times this leads to my downfall. I take a 1v1 fight and I end up losing a lot more health and am forced to Flash away or Q away.​I am using the Runes build from Mobafire cause my friend suggested it. It's Conqueror, triumph, Tenacity & Coup de grace. I don't understand Runes that much or what tenacity is. Are these the correct runes?What items do I build and in what order? I have never understood this. Some places I read Trinity force and some say Black Cleaver. Some even mention Duskblade but I am always lost on what to build first.When do I take a 1v1 and when do I avoid? If I do take it, how can I ensure that I at least do damage without getting rekt? Do I auto first into E and then Q? When do i W in a fight?If anyone can help me with this, it would be great! via /r/GarenMains https://ift.tt/34z8vtl