The video below below explains what acceleration is using an example of a race car that starts from 0 km/h and after a race, has a velocity of 150 km/h.  Acceleration is the change in velocity over a period of time.  To calculate acceleration, you use the change in velocity and divide it by the change in time.

The video below helps to explain constant velocity by showing it on dot diagrams.  Dot diagrams express the change or constant velocity by looking at the distance in between the dots.  The video also focuses on the difference between scalars and vectors.  Scalars only take into account magnitude (eg. 30 m/h) and vectors take into account magnitude and direction (eg.40 m/h north).