Question about the progression of getting a rank

For example, your currently unranked and now your starting your first rank games. how does the matchmaking determine what sort of player you would be fighting and paired with? and lets say your new to league as well so you did not have a previous rank last season or any season. How does that exactly work?

the reason why i ask is because i take a look at my teamates match history sometimes and notice a couple of things that i knew was just not right. So currently i am a bit salty from a game where my malphite didn't seem to know what he was doing. but i didn't get mad at him i thought it was just a bad game but i decided to take a look. What i find is that his starting his new rank games and i know scores and related in-game nature doesn't mean everything. But most of his games were poor and finding things such as him building a hydra on a garen? i'm all out for some out of meta stuff and all but it was very clear he was new to the game and perhaps rushed into rank.

Now i'm questioning the matchmaking system not saying its garbage or anything but curious how does it work? or is it really flawed? I just wish to know so that i don't keep questioning it to myself.