Absolute value is how far away a number is from 0. So basically, if a number is positive leave it as it is, if it's negative make it positive.
Modulo is the remainder when you divide. So, say we want to divide 10 by 3. 3 goes into 10 3 times, with 1 left over. That 1 is our remainder, so 10 modulo 3 (denoted 10%3) == 1