What is Chromatography?

Chromatography basically means separation.
A stationary phase is coated either onto a column or a flat surface, can either be a solid or a liquid that is of a polar or non-polar nature.
The mobile phase which is a liquid or gas, contains your mixture, that contains your analyte, is passed through the column or flat surface is dipped into mobile phase and a series of interaction occurs.
There is an equilibrium between mobile and stationary phase such that the mixture is separated into its individual components as time goes by.
Like attracts like, so if stationary phase is polar the most polar component in your mixture is retained the longest and comes out last. And non-polar stationary phase retains non-polar component longest.
In Gas Chromatography and Liquid Chromatography, detectors detect the different components as a signal and gives a Chromatogram which shows different peaks which is related to your components and from that, the amount (concentration) can be calculated via integration and comparison with standards of known concentration.
A Chromatogram showing the different peaks of different components that were separated:
Image from: http://ishigirl.tripod.com/pchem/gc_ms.html
Hope this helps 🙂
A video on chromatography paper.