I'm surprised you didn't come across chromatography in chemistry at school. It's where you, say, put a drop of ink on filter paper, then dip one end of the filter paper in water; and as the water travels along the filter paper it carries the different components of the ink along with it at different speeds, depending on the sizes and shapes of the different molecules. It can thus be used as a way of separating a mixture of chemicals out into its individual components.