How do we add and subtract negative numbers?

Well, for numbers, we have a number axis which is a straight line (like this [...]) and it is divided into more pieces, of one unit each. We begin to draw this axis by placing zero in the middle (like this [...]) and then placing positive units (1, 2, 3...) on the right side, and negative numbers (-1, -2, -3...) on the left side.

Looking at the axis, if we have 2 - 1 it means we are at the second unit and we go to the left with one unit (subtracting one). Now, applying the same principle, if we have 2 - 3, it means we go to the left with 3 units and we arrive at -1; hence, 2 - 3 = -1. When we add, we move to the right, for example: -5 + 2 means that from the -5 point on the line we move 2 units to the right; hence -5 + 2= -3.