You are asking how to label the points where the line crosses the axis, is that correct?
Like Andy answered you, your slope is -1, (or -1/1, rise over run) and your y-intercept is -4 (since y = mx + b).
Since you know that you have a point at (0,-4), you can then use your slope, -1, to find another point on your line for this equation. From the point (0,-4), you would move down one unit ( -1 "rise") and to the right 1 unit (positive 1 "run"), placing your next point at (1,-5). You mark both of these points with a very small circle or "dot" and connect the lines with a ruler, putting an arrow on each end since it goes on forever.
If this doesn't answer your question, please let me know and I will clarify!
Hope this helps!