Speed does not have direction. So it is a Scalar quantity.
Speed is measured as meter ( distance) / second (time).
The unit for speed is m/s . (read as : meter per second )
Displacement is the same as distance, but it has direction.
The only difference between speed and velocity is that velocity has direction, speed does not.
So Velocity is a Vector quantity.
The unit of velocity is meter / second or m/s , similar to speed.
Direction may be shown by a + or – sign.
Acceleration has direction. So it is a Vector quantity.
+ or – sign can be used to show whether acceleration is increasing or decreasing.
A negative acceleration is called a Deceleration or Retardation.
Acceleration is measured in m/s². ( read as : meter per second squared )
[ meter/second (change in velocity) / second (time)]
Read more about speed, velocity & acceleration at the physics classroom.
Watch this youtube tutorial to understand better.