New Player

Hello, I am fairly new to this game and I want to know if anyone has any advice to improve my game play. I have recently been playing Poppy a lot and I want to know if anyone has tips for me to get better at her. I also want to find an adc ranged champion, but I am having trouble finding one that matches my playstyle. I have tried Sivir many times, but I am HORRIBLE at her. So, does anyone have any recommendations for that? The link is for my match history. Also,I have recently tried to use replay.gg, but I cannot get it to let me watch the replays I want to. Finally, I would like to know how to craft. I have 2 key pieces, 2 boxes,a Jarven and a Garen skin, but do not know how to use them... I do not know anything about crating,so any information on that would be great! Thank you very much!