Placements matches and how they work?

Hello LoL community. :) Returning player here, haven't played competitively for few years, and would like to know more about placement matches.

So my question is what factors play role in my final placement after 10 matches? Do K/D/A play a role? My score after a match?

I know thete is no official statement from Riot about that, so i am looking for any general knowledge...

Thank you in advance :)