When graphing an equation, start with the y-intercept. For this problem, the y intercept is 3, so our first point is (0,3). Since the slope is -1/2, to the right of the point, move 1 down from the intercept and 2 to the right. Now, to find points on the left of (0,3), move up 1 and 2 to the left. Keep doing this until you have enough points to form a line.
