You can find the slope either by just looking at the line or using the slope formula.
#1: The slope formula is:
Find two points and plug it into the formula
I will use (0, 2) and (1, -1)
(0, 2) = (x₁, y₁)
(1, -1) = (x₂, y₂)
[two negatives cancel each other out and become positive]
m = -3
#2: To find the slope without having to do the work, you use this:
Rise is the number of units you go up(+) or down(-) from each point
Run is the number of units you go to the right from each point
If we start at a defined/obvious point, like (0, 2), find the next point and see how many units it goes up or down and to the right. The next point is (1, -1), so from each point, you go down 3 units and to the right 1 unit. So your slope is -3/1 or -3. You can make sure the slope is right by looking at another point.