Constant Velocity: Constant velocity means that the object in motion is moving in a straight line at a constant speed. This video demonstrates constant velocity. The cart moves at a uniform motion as the speed is neither accelerating or decelerating.

https://youtu.be/u8qVRAzMaxY

Acceleration: Acceleration is the rate of change of velocity of an object. In this video we see a fighter jet accelerate from the ground off into the air. It is accelerating because it was slow while driving on the ground and then sped up to gain enough speed to go airborne.