the position velocity output will give you a vector that represents the movement of the object from the last frame to the current in units/second. A position velocity of (100/-200/300) would be a movement of +100 units on the x-axis, -200 on y-axis and +300 units on z-axis within one second. To calculate the frame to frame speed you have to devide this by the FPS setting you can get from the time node.
Same goes for rotation velocity using radians.
If you want the velocity based on a specific frame base you can use the previous positon/rotation node. History depht has to be set to a greater value then history level to store information on the set number of frames.
By calculating the difference between position and previous position you get the velocity with the set frame number (history level) as base.