Explain the difference in meaning between |-3| and -3

Answer 1

-3 means the number 3 units to the left of zero
|-3| just means how far away from zero 3 is, regardless of direction.
|-3| = 3

You would do well just always to remember just what the definition of |x| is:
|x| = x if x >= 0
|x| = -x if x < 0