Colligative properties refer to how dissolving a solute into a solvent affects the solvent's physical properties. Specifically, it lowers the vapor pressure and freezing point and raises the boiling point. These effects are due to interactions between the solute particles and solvent molecules. The greater the number of solute particles, the larger the impact on the solvent's properties. This number depends on whether the solute is an electrolyte or non-electrolyte. Electrolytes dissociate into multiple ions in solution, whereas non-electrolytes remain intact molecules. The document provides examples of calculating the changes in boiling point and freezing point based on molality and other factors.