When you are graphing, you need to remember that mx is the slope, and b is the y intercept. Since the y intercept is 3, you place your first point at (0,3). Now since the slop is positive one, you will go right 1, up one and place a point, and then right 1, up one and place a point and so on. You can also extend the line farther down by going left 1, down 1, etc.