A scalar requires only magnitude to define it, in other words just one statement about size is required. For example temperature in a scalar, only one comment about size is necessary; it is 14 degrees Celsius. The same can be said for time: it is 2pm.

A vector however requires both magnitude and direction to define it, for example a force is described by both its size and the direction in which it is acting.

One last example we can describe a car's speed as 40mph (speed is a scalar), but to describe a car's velocity (vector) we must add a direction, e.g. 40mph in the direction South East.