what is the tie breaks for in a tournament chess game?


What is it for?
To determine a "winner" using the fairest method possible in the event of a tied score.
If you are interested in the method used in Chess.com tournaments, read this, which comes from the Help page:
What happens when there is a tied score? And what is the Tie Break?
https://support.chess.com/customer/portal/articles/1444840