The slope between (x1,y1) and (x2,y2) is (y2-y1)/(x2-x1)
given
(-3,3) and (1,-5)
slope=(-5-3)/(1-(-3))=(-8)/(1+3)=-8/4=-2
the slope is the rise/run or change in y divided by change in x, from left to right
so
(-3,3) to (1,-5)
(x,y)
from 3 to -5 is down 8 or -8
from -3 to 1 is up 4, or 4
rise/run=-8/4=-2
slope is -2
A parabola in mathematics is basically plane curve which is mirror-symmetrical and is approximately U-shaped. A point and a line in a U shape.
Example below: