Why am i so bad at LoL?

First of all, I'm not even sure if this is the right thread to post in ect. but i dont know where else to turn. Ok so im a player of league of legends and i have been since i believe early season 3 i cant remember (A Long Time) Anyway i feel like i still play quite bad dispite playing this game for so long. I have only about 800 wins in normal and i feel like i still play like someone who's like lvl 20. I don't have much knowledge of the things i should from playing as long as i should. For example when i should build certain items and when i should do different things. I don't know how to freeze a lane or do a lot of mechanical stuff in game. I really need some help because i feel like i'm a quite bad player for my playtime. Please, some help would be appreciated. I really need to learn these things. I have friends who started playing a long time after me and still proceed to always play better than me and have a lot more knowledge of different things. I apologise if this doesn't make much sense or it's hard to understand. Thanks in advance.
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