Velocity is a vector since it is composed of a quantity of speed and a direction. Velocity is defined as the rate at which an object's position changes.
The direction of the velocity vector is simply the direction that the object is moving. For example, it is not sufficient to say something has a velocity of 20 miles per hour, when this is only the scalar quantity of speed. Adding a northward direction, this becomes a velocity of 20 miles per hour northward. It is important to note that since velocity is a vector quantity, operations, such as addition, subtraction and dot product, are not the same as scalar quantities.