The absolute value of a number means how far the number is from 0. We use absolute values when we only care how big a number is, not whether it's positive or negative. To indicate an absolute value, we put '|' signs around the number, like so: |3|.
To find the absolute value of a number, just take off the negative sign, if there is one. If there isn't one, just leave it alone. For example, |3| = 3 and also |−3| = 3. For this sort of problem, 0 works the same as any other number; |0| = 0.