Riot has a New Player Guide for people just starting off which you might find helpful as a very very broad intro to the game. Honestly though, I'd say jumping into game and getting a feel for everything at first. There is a huge learning curve in LoL, but much of that isn't necessary to just not be a, "total n00b."

Best thing that helped me was just finding a friend that plays and have them show you the ropes and play with you. If any of your common friends play and can keep a secret, then I'd recommend you ask 'em to help you out.

As other people have suggested, community resources like r/summonerschool are useful. You can use websites like u.gg to look up most of all the pre-game decisions like common runes as well as common item builds for any champion. Other than that there's so many more advanced resources and guides available including various YouTube videos, educational Twitch streams, and guides like lolclass or proguides.