Chromatography involves separating mixtures into their components based on how they partition between two phases, a stationary phase and a mobile phase. The different affinity of components for the stationary phase causes separation over time as they travel through at different rates. Key types of chromatography include liquid column chromatography using columns packed with particles, gas-liquid chromatography using an inert gas as the mobile phase, and planar chromatography techniques like thin-layer chromatography using coated plates.