Scalar: A quantity that can be specified fully by mentioning its magnitude(or value). For example, saying 350 K completely specifies the temperature to be 350 Kelvin and 300,000,000 m/s specifies the speed of light(approx.).
Vector: A quantity that can only be specified by mentioning its magnitude as well as direction. For example, 30 km/h to the West is the complete specification of velocity.
Watch the video below to learn more (credits-TED-Ed):