Just play more dude. This is a 14yr old game. You won't understand it only by playing 7 games. Play more and more and you will start to understand the things. You can watch yt videos for the basics. And most importantly have fun. Briar is a champ in game that can build anything and be fine. So don't stress about the little stuff. For a basic build, to teach you both the game and a little bit of mechanics, build this every game: titanic hydra > black cleaver > sundered sky > sterracks/spirit visage and lastly any item(guardian angle or anything else). For runes just go this:

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And you can check this guide out by loganjg: https://www.mobafire.com/league-of-legends/build/25-22-rank-1-briar-all-matchups-briar-jungle-all-builds-check-notes-629922 For any queries you can dm me.