Any useful detailed tutorials on game performance and draw calls for beginners in game development?

hi.. I am new to game development and unity . I am in a project developing a sort of car game. And now my team has come to a stage where game performance has become a big problem . I have spent a lot of time reading about draw calls but could not really find any detailed tutorial for beginners. Can somebody suggest me some really helpful tutorial regarding game performance and draw calls ? May be a detailed tutorial on designing , modeling a full fledged arena for a game can help. I would really appreciate anyone's help in this regard.