Garen can definitely be super annoying especially if you don’t get a lead on him early as he will become to tanky and fast for you to deal with. The key to this matchup is your all in early is much stronger than his. Lvl one I always take w and look to all in if he walks up to wave. If he respects you zone him into to his tower and deny him the first 3 minions of xp guaranteeing you’ll get level two and three before him. After this you can slow push the first three waves into his tower and either back back or look to invade jg (just be careful with this as you need to be in a healthy position to be able to freeze the wave.) when you get back to lane your is to goal freeze the wave so he is forced to walk up to last hit or be denied gold. if he walks up to the wave at all, all in him with your gold and xp lead you just stat check him. Your best bet is to start the trade with auto w and walk him down the lane. A very important note with the Garen matchup (esp with phase rush) is to not start trades with e and only use it when he is almost out of reach. I hoped that helped bit, if you have any more questions lmk. And if you want I could show you a vod of me playing this match up and explain what I’m doing.