One way you can find the slope of a line is through counting.
Start on one point, then move your finger down/up until you are right next to the other point. Make sure you count how many points it was from the original point.
Next, move your finger sideways from where it was, landing on the point. Count how far away it is. If you moved to the left, the number is negative and vice versa.
Put the two numbers you counted in a fraction. The first one you counted is the numerator or top number. Then you have the slope.