1. Shading is a technique using a shadow/darker colors to have variation in your art. Your base color is the lightest all and you are making those shadows to make shapes, variation, curves, and many other things that imitate reality.
By this you can control the dark parts and also the light parts of your artwork to imitate what the real world is because by the end of the day art is something creative made by human that imitate what he/she can see using his/her mind to create those art, design, graphics, etc.
2. Tinting is a technique using light to have variation in your art from flat color and brightness. It is a complete opposite of shading. Your base color here is the darkest color if possible.
By combining these two technique you can create a Toning Technique. Toning is simply means the combination of these two techniques. Your base color is the middle tone/colored/level then you apply shading for creating shadows and apply the tinting for creating lighter parts and the areas where that subject of yours in the artwork expose to light.
In real world Tinting is the best technique to follow but for artist Toning Technique is the most effective way to create art that consider lighting in the artwork. However, shading is used mostly on traditional art since most of our canvas, paper and other materials were made up of lighter surface and using darker mediums to create art.
Whatever your technique is stick with it, there's no bad technique but knowing this may help you create your art more effectively depending on the available materials or some limitations you have in art.
Hope this give you few information about these techniques. These were very basic techniques every artist should know.
