How do I distinguish "above-the-line", "below-the-line" and "through-the-line?

Answer 1

Like this:


above
--------------------------


or

---------------------------
below


or

-------------through--------------

Answer 2

Points earned for overtricks, level bonus, double and redouble bonus, and penalties are entered below the line. Contract points are entered above the line.

If you're entering points through the line, then you're doing something wrong.