Q:

What is the actual difference between scalar and vector quantities?

We often differentiate them by saying scalar quantity have magnitude while vector have both direction and magnitude. But how's it possible that if an object is moving then it won't have direction in case of scalar quantity?

A:

But how's it possible that if an object is moving then it won't have
  direction in case of scalar quantity?

A scalar quantity is simply a number. But a scalar quantity can be associated with a vector quantity. In such cases the scalar quantity is the magnitude of the vector.
If you are driving a car the speedometer gives you its speed (mph or kph). But if you are only looking at the speedometer and not the road (and you shouldn't!) it would only be a number. It's only when you look at the road (or perhaps your Nav) when you can then determine the direction of the car, and when you are able to associate the  speedometer reading with the velocity of the car, i.e., the magnitude of its velocity. 
But not all scalar quantities are the magnitudes of vectors. Examples are time, mass, energy, and temperature to name a very few. 
Hope this helps.

