one big issue is, the system does do it's best to match you with people of similar skill level, however, (this is a severe problem without a very good answer) very often low levels are filled with people in gold or higher ranked who just got bored and wanted to make a new account. so even though you may be a level 15 summoner vs a level 5, if that player is platinum or even diamond, you've very little chance to get by. sadly there is no good way to fix this besides just do your best and don't let it get you down, league takes a lot of time to learn even the basics
i'd recommend practicing bots for a while, if you're having a decent (easy) time, set yourself some limits, try not to go back until you die, try to only cs and never hit opponents, try to always be auto attacking, constantly (you'll be shoving the wave into their tower) while hitting opposing champions as much as possible, these aren't insta win skills, but they can be very good to learn and good practice if you're having trouble with pvp, but not much issue with pve
one of the most important skills to learn: last hit, about 15 minions = 1 kill's worth of gold
use your trinket... even if you don't see many people, try and make a point of warding a bush in the river every time it's on cooldown... learn this skill now and it will take you far
i highly recommend taking just 2-3 champions at most (or maybe even 1) that you really like and focusing on them. especially at low levels, don't grab a new champ and go to pvp, as someone who knows their champ better will simply wreck you. pick a few champs you really like and try and get as good as you can with them, the better you know your champion, the better you can do, even if you don't know the opponet's champion very well, if you say 'i know my champ can do about 300 damage" and they have 400 hp, you know that's not enough for a kill (once you get more experienced, it's recommended to learn at least 1 champ for every role, though some can overlap, like poppy can jungle or top, for example)
i mean no offense, but i also recommend staying away from the jungle until you're at least summoner 20+, either that or stick to simple champs like warwick in the jungle. the jungle is very difficult without a lot of experience and the runes/masteries to back it up. also, especially at low levels, people will often blame the jungler if they think they're having a bad game, you've been warned