The absolute value of any number is its magnitude regardless of whether it is positive or negative. So absolute value is always positive.
It's the same as taking the positive square root of the number squared. So the absolute value of 10 and -10 is 10, because both have a square of 100.
If we take a straight line and mark its centre point as 0, then numbers to the left of centre are negative and those to right of centre are positive. Taking the absolute value is the same as measuring how far the number is from the centre point. -10 is 10 away from zero and so is +10.