I am a newer player as well, started at the end of August, looking at your match history and profile, pick 2-3 champs that you feel you do well with.
Stay away from ranked for a month or 2, and learn those champs, once comfortable, expand your roster of champs you enjoy.
Myself, i didn't play a ranked game for at least 2 months, maybe longer, If you like Support, blind is not bad to play in, rarely do you get contested for support, and once you start to play draft as a support main, you are autofilled protected, and 99.9% of the time you will get your role.
check some build paths and guides on these websites.
https://lolalytics.com/ranked/worldwide/platinum/plus/home/
https://www.mobafire.com/
and if you search the champ you want to learn on youtube, good chance you can find some guides, some of the youtubers do a good job on explaining how/why they play the champ you are interested in, not just this sweet looking pentakill, and not explaining the hows and whys they do certain things.
(Just make sure to filter the results for the last month or 2, no use watching a video from 2 years ago, since the game is constantly changing)
Just my 2 cents offered here, but don't rush ranked play to early, you will just get frustrated and it will take the fun out of the game.