The phrase "to dissolve the sugar" means to mix or blend sugar with a liquid, such as water or milk, until it is completely broken down and dispersed evenly throughout the mixture. This process can be done manually by stirring the sugar into the liquid with a spoon or whisk, or using heat or an acidic ingredient like lemon juice to help speed up the dissolving process. Once the sugar has been fully dissolved, it will no longer appear as separate grains but rather will be evenly distributed throughout the mixture.