In this definition we will think of |p| as the distance of p from the origin onto a number line. Also we will always employ a positive value for distance. Assume the following number line.
From this we can get the given values of absolute value.
|2| = 2 |-3| =3 |9/2| = 9
All that we have to do is identify the point onto the number line & determine its distance from the origin. Note as well that we also have |0 |= 0 .