[Question] Can someone explain the Elo system to me?

First Q. How are placements decided? Is it purely win/loss? Does it include K/D? How about Objectives?

Second Q. How are team match ups made? How do they balance who is on a team? I feel like I OFTEN either have a platinum or better player on my team or against me.

Third Q. Is there a way to get more LP for matches? Can I increase my gains?