http://www.youtube.com/watch?v=VEz2Xm6zrW0&feature=fvst

This video shows both acceleration and velocity.
Velocity is the description of how fast something is moving and what direction they are moving in. The formula for velocity is; velocity equals distance over time. It describes the change in speed and direction. If a car, such as the car in this video, continues on a straight road, and is going at a speed of 80mph. It will continue at a constant velocity unless the velocity is increased or decreased. Changes in velocity occur when a car goes around a turn or hits the breaks.
Acceleration is how quickly velocity changes. The term acceleration applies to both the increases and decreases in velocity. Acceleration equals the change of velocity over the time interval (or the time it took to change). On this circular track, although the cars may not be increasing or decreasing their speed their acceleration is still changing due to the circular shape of the track. This causes a change in pace in which the car is going.
If something has constant velocity it cannot have constant acceleration because constant acceleration means its getting faster where as constant velocity means its staying the same. Constant acceleration means an object such as the car is covering more ground per time interval where as constant velocity means the car is going at the exact same speed. So if the car in the video is going 60 miles per hour its acceleration is increasing where as its velocity is constant.