Think of the sea level as 0. Anything above the sea (like a flying bird) is positive (+), and anything below the water (like a swimming fish) is negative (-). Addition (+) means moving UP, and subtraction (-) means moving DOWN.
0 is neither positive nor negative. It is the special reference point for everything.
The sign (+/-) shows the 'direction', and the number shows the 'distance' from 0. This is called the absolute value.
Subtraction means 'turn around', and negative means 'move backward'. So, 'turning around and moving backward' results in moving forward (positive).
Formula
Let's check your understanding!