What does a velocity vs. time graph show?

Velocity vs. time graph shows the variation of velocity with time.
If the velocity-time graph is a straight line parallel to the x axis, the object moves with constant velocity.
If the graph is a straight line (not parallel to the x axis), the velocity is increasing uniformly i.e. the body moves with constant .
The slope of the graph at any point gives the value of acceleration at that point. The steeper the curve at a point, the greater is the acceleration.