You're only lv 13, so I'd recommend just spamming normals to get used to the game. If you're worried about people yelling at you, you can mute the chat by hitting esc in-game (practice tool is a good way to do this without afking) and looking at the screenshot to find the option. I assume you're talking to people over discord anyways since you said a competition was happening, so you won't be missing out on anything anyways.
There's this site called op.gg
that I always have open on my other monitor while I play, though there's an app for it too if you don't have one. You can look up your character and it'll give you whatever standard item build path plus rune setup is popular right now (though the new recommended item system in league is really good, so you can get away with only using op.gg
for runes). Make sure you avoid unsealed spellbook, though. You can also look up other players on op.gg
Focus on practicing cs (I like to go into practice tool for 10 minutes a day just last hitting minions while my level is locked at 1) and watch all the replays for your games at the end of the day, focusing only on the times you died in laning phase (aka before 15 minutes), what led you to those deaths, and what you need to work on to avoid those situations in the future. Even if you don't get a kill early, just surviving lane while getting a decent amount of cs and not dying will put you in a position to carry as your opponents tend to give you free kills. After 15 minutes, the game turns into aram, so focus on only taking fights when your team is grouped together and hopefully alive.
Sorry for being an autist, but I've put far too much time into league to not be one. Hope you enjoy the game!