Slope-intercept form:
y = mx + b
"m" is the slope, "b" is the y-intercept (the y value when x = 0, or (0,y))
Rise is the number of units you go up(+) or down(-)
Run is the number of units you go to the right
y = -2x
This has a y-intercept of 0, so the line intersects the y-axis/goes through the origin at (0,0)
The slope is -2 or , so from each point, you go down 2 units, and to the right 1 unit.