point-slope form is y - y1 = m(x - x1). (x1, y1) is any point on the line, and m is the slope. x and y are your variables.
so, (x1, y1) can be either of the points your problem lists. those are given to you. what you need to do is find the slope: m = (y2 - y1)/(x2 - x1). use the two points on your graph, (1/2, 2) and (-3, -1) for the xs and ys.
m = (-1 - 2)/(-3 - 1/2) ... simplify inside parentheses
m = (-3)/(-7/2) ... to divide by a fraction, flip the second one and multiply
m = -6/7
so your slope is -6/7. from here, you simply plug it into point-slope form and choose either of your points:
y - 2 = (-6/7)(x - 1/2)