Another way is with Epilog:
Epilog
Plot[(.25 x)^3 + (-.4 x)^2 - 2, {x, -10, 10}, AspectRatio -> 1, ImageSize -> {{480}, {540}}, Epilog -> {PointSize[Large], Point[{0, 0}]}]
This also seems to be what I need. Thanks, Gianluca. As I go forward, I will try to gain an understanding of both Show[] and Epilog->.
That's just what I needed. Thanks! (I didn't even know the function Show[] existed.)
Use Point and then combine it with the plot using Show.
