Orthographic scenes are specified in ways similar to perspective scenes. Issue the command
Ortho(left, right, bottom, top, near, far)
which specifies the four corners of the near plane, the distance to the near plane, and the distance to the far plane.
If you are dealing with a simple 2-D environment, you can set up a two-dimensional orthographic scene with the command
Ortho2D (left, right, bottom, top)
which specifies the corners of the two-dimensional view.