Cut the top of the bottle as shown, Put 200ml hot water in the bottle, stir with 50gram brown sugar. Put the sugar water in cold water to cool it down til 40C (temperature), They use a bigger container with cold water - put the small cup that they use to make sugar water in that container and that stick is a thermometer because they want the sugar water to cool down to 40C (temperature), After cooling down, put the sugar water in the bottle then add the yeast, No need to mix the yeast with the sugar water. When yeast ferments, it creates carbon dioxide.
via diyhappy.com