Pastels are powdered sticks of pigment, binded together. They are rubbed across paper which leaves the colour behind, and a paint-like finish, but with more control and a unique feel than standard paints, with no variation from the colour of the natural dye.
Pastels can be bought in many different colours and combinations, often with different finishes, which all comes down to trial and error to try and find the pastel that meets your personal preference. A great traditional art form thats created some world class pieces over the years.