What is the difference between a vector and a scalar quantity?

A scalar quantity is one that has a magnitude (size) only, and no associated direction in which that size 'points'. A good example of a scalar is temperature, because temperature has a size (for example 20 degrees), but no direction. A vector quantity, on the other hand, has both a magnitude (size) and a direction in which that size points. An example of a vector is force, because a force has a size (for example 10N) and also a direction, as that force can act to the left, the right, or any other direction.