If you want the definition of absolute value, it is defined how far a number is away from zero.
Geno's answer should help you to understand specific examples.
If the number is zero, its absolute value is zero. |0| = 0
If the number is positive, leave it as it is. |3| = 3
If the number is negative, turn it into a positive number. |-5| = 5
Absolute value dosn't really effect positive integers seeing as they become the same number. Negative integers, though, are changed to their positive. For example, /-24/=24, /35/=35 /14-15+12-5.5-6/=0.5
If you want the definition of absolute value, it is defined how far a number is away from zero.
Geno's answer should help you to understand specific examples.