Motion is described in terms of time and distance and it signifies that the object is changing its position with respect to a reference point. The well known example is our Earth. As we know our Earth is always in motion, although, for us it seems to be in still position.
Speed and velocity, these terms gives us an idea of how slow or how fast a body is moving. Quite a few times, we need to know which one of the two or more objects is moving faster. One can easily tell which amongst all the vehicles, that are moving in the same direction on a same road at any instant of time, is moving faster. But if their direction of motion is opposite to each other, we may not be able to make out which of the vehicle is moving faster. One must have the better understanding of the concepts of velocity to study the motion of any object.