What is the difference between i-3i and -3

The absolute value of a number is its distance away from 0. An easy rule to remember with absolute value is that it makes negative numbers positive, and has no effect on positive numbers.

Therefore, |-3|=3 while -3=-3.

The absolute value just tells you how far away the number is from 0

so |-3|=|3|=3

|-3|=3 but -3=3

the difference is that the first one tells the distance while the 2nd one is including the direction (to the left of 0)