How to create a game test plan for a single screen game?

I'm required to create a game test plan for a single screen game (this is my first time). Its a simple game whereas the user has to click at the correct time to collect gemstones with a swing winch hook. In order to win the game the user has to collect hundred dollars or more worth of gemstones within the timeframe of sixty seconds. I am confused as to where to start from, I've tried searching online but all I'm getting is complicated layout structures. Can someone please assist me?