Backgrounds:

When modeling a scene it is sometimes easier to create a static background for your scene than to create a 3d background yourself.  In maya you can use different kinds of backgrounds attached to the camera so that wherever that camera looks it will always see the same background.

To create a background you create what maya calls an image plane.

To do so create a new camera by going to Panels>Perspective>New

Now with your mouse over the new perspective window go to View>Select Camera

Open the attribute editor and find the Environment options.  Click on the Create button next to where it says, "Image Plane"

Now in the imagePlane1 node go to the Image Name section and browse for the image you want to use as the background.  This is just like using an image as a texture.

Now go to Panels>Pespective>persp to switch back to the other perspective view.
In your scene you should be able to see a camera and a large square with an x in it just like the one below:
(You may have to move around a bit before you can see both the camera and the image plane.

If you rotate your camera around you will see that the image plane is always infront of it.
You can use the same method to use a flat or gradient color as the background.
 

Atmosphere

In order to add a more realistic feel to your scene you might want to add some environment fog.  To do this simply open the Render Globals window and go to RenderingOptions>Environment Fog

Click on the map button next to Environment Fog.
When you click the button maya automatically creates the environmentFogShape1 node with default values.  To change the values of the environmentFogShape1 node click the input connections button which now appears where the map button used to appear.

This will open the attribute editor for the envFogMaterial.  In here you can change all of the attributes of the fog.  I have only changed the color and the saturation distance.

I also added a directional light to the scene.

Here is my rendered scene with fog:
 

Transparency

Changing the transparency is very easy.  Just select the shader you wish to make transparent and move the transparency slider:

And the rendered image:

more Maya tutorials
comments..suggestions..questions:  josh@occipital.net