Half the problems are a bare absolute value - |-11|, |8| - and half put one operation after it: |11| - (-6), |5| + 2. The bars are always taken first, which is the whole idea: |−7| is 7, and what happens next is ordinary arithmetic.
Answers can still be negative. |3| - 8 is -5, because taking the absolute value of the first number does not make the rest of the problem positive. Students who read the bars as "make everything positive" rather than "how far from zero" get those wrong, which is exactly why they are on the sheet.
How far a number is from zero, ignoring direction. |-7| and |7| are both 7. It is a distance, which is why it is never negative.
The absolute value itself never is. The answer to the whole problem can be: |3| - 8 is -5. The bars apply to what is inside them, not to the rest of the line.
Sixth grade, alongside first meeting negative numbers and putting them in order. It is usually taught in the same unit.
As two upright strokes around the number: |-7|. On these sheets they only ever wrap a single number, not a whole expression.