Stuck on game socket challenge

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I am very stuck on this final challenge and cannot figure out the game logic for myself. I was successfully able to code the socket.io functions to allow multiple players to join and move with controls, but after that, I am lost. Question is, where can I learn some of this game logic with canvas? Is there certain documentation I can find or a tutorial? How can I make a player avatar, make the coins count for points, add styling to the canvas, scoreboard, etc? Thanks in advance.

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Challenge: Secure Real Time Multiplayer Game

Link to the challenge: