I need help getting started in DND as a complete newbie

So, I'm really not expecting anything from this post, honestly this is just a desperate attempt at getting any sort of guidance as a complete and utter newbie who just got invited to my first ever DnD group in my fresh 21 years of existence, the session 0 is in 3 days, and im just now realizing the rabbit hole to understanding the rules is much deeper than I once thought, so I'm just dumping everything here and whoever is kind enough to give any sort of advice on how to understand... p much everything (i've watched a couple videos, attempted to create a character in the official DnD Beyon website and understood almost nothing, read on all the classes and im still confused on how these can interact/affect the species, and im still very confused on the whole stats thing, there's just so much info that my brain has a hard time understanding it all) i'd greatly appreciate any sort of help

on a sidenote, this ain't mandatory, but would still love some help, i feel like i have a bit of issues creating a character for DND, or more less, i have a pre existing Original Character of mine that i want to ''translate'' into DND but holy crap im also still very lost on how to translate my character into the pre existing races and setting already established, since my character is pretty modern based

uhhhh yeah anyways, ty to whoever reads/comments, also a newbie on reddit in general so sorry if i say the wrong thing