What's a new player to do?

As context, I've started to play the game properly (that is, not playing one game of co-op, saying "I have no idea what's going on and nobody's helping" and left) for a week or two now, and I feel that I have to get this off my chest and see if there is something I'm missing.

After playing for the short time that I have with a group, I have immediately discovered how unfair this game is to a new player. The group consisted of four of us; myself, a friend who was a few levels higher, and IIRC two around the 20-30 mark. We were paired with, on our team, an Ekko who was around my level also, if not lower.

The enemy team consisted of three level 30s and two level 24s. I ended up against a Renekton who I physically couldn't harm at the start of the game playing as Vladimir. At the beginning of the game, I was pushed immediately into tower and couldn't even touch a melee opponent because whenever I came into my range, he would burst forward and cut a third of my health off, while I did a measly tenth, and then just walk back to his minions and carry on. Later in the same game, I couldn't farm whatsoever because as soon as I went into range of a minion, he would dive me, stun me and subsequently hit me for my entire health within a second, before level 6. Alongside this, the Ekko on our team and the other player my level were also completely battered by an opposition who was higher level than us. Subsequently, at the end of the match, the first thing the Renekton says is "such an easy game", after my retort stating how this is such a nice game to new players, he said became somewhat apologetic and said "You just have to stay in tower". What I've been told by my team is that because I am not level 30, I cannot push, I cannot poke, and the only thing I am actually permitted to do is sit in my tower and try not to die so that the guy I'm against doesn't get fed. All this time I have to watch the other player continue to outlevel and outfund me until ultimately he just decides that he's bigger than me and jumps me in tower. Afterwards we even discovered that one of the players we were against was actually a Platinum player.

After that game, I took a minute to look at what getting to level 30 actually means, and what I saw was absolutely terrifying: A level 30 gets to run around with what can quite simply be stated as nearly two starter items for free at the start of the game. Before the game has even begun, I am being outmatched by my opponent because, and this is as point-blank as it can be, his numbers are bigger than mine, always.

Now what I really want to know is how in God's good earth I am actually supposed to enjoy this game and do anything. At the moment, I have never been in a single position where I've considered myself on equal grounds to my opponent in lane. Is there something I'm missing? Is there a different mode in which runes and masteries are not present? Am I doing something wrong? Honestly, this game just seems so unfriendly to new players, both in community, balancing and the actual gameplay itself.

What am I missing?

TL;DR: Because I'm level 10, I'm losing because I'm getting pitted against people with bigger numbers than me. help?