If you are interested in starting practicing with pastel painting, it is recommended you start with a good type of pastels. Low quality pastels are very difficult to use and will ruin your experience with this kind of amazing painting style.
Soft Pastels have a very high concentration of pigment that is held together by the least amount of gum binder as possible. As a result, they crumble very easily, but their colors are wonderfuly intense. They are Great for shading, and detailed Paintings.
Buy a set of those wonderful soft pastels and jump in to the amazing world of pastel painting!