The slope of a line measures how steep it is. Think of a hill. On flat ground, there is no slope, so the slope is zero. On a very steep hill with a slope of 1, it means that for every step forward you go, you also go up one step. So the slope measures how far up or down you go as you move a given distance horizontally. We often say that the slope is the "rise" (vertical distance) divided by the "run" (horizontal distance).
Given two points, (x1,y1) and (x2,y2), the x's are the horizontal coordinate (run) and the y's are the vertical coordinate (rise). The slope is designated by the symbol m and its formula is:
m = (y2-y1) / (x2-x1)
You are given two points, so plug them into the formula to get the slope. It doesn't matter which one is (x1,y1) and which is (x2,y2); you'll get the same answer.