Welcome!
Modify mybot.js to start writing your bot. Opening game.html will allow you to generate random boards, and either watch your bot play or step through one move at a time. Refer here for available methods. gl/hf! - Scribd.
ps: you should be able to ignore everything in assets/, but if you want to disable the opponent bot from playing in game.html, go to assets/simplebot.js and find:
makeMove: function() {
// to disable to opponent, uncomment the next line
// return PASS;Uncomment return PASS; and your bot will be free to roam the board alone.