You will first need to create a new camera and then attach an image plane to it.
Create a new camera by selecting Create > Camera.
Translate the camera 2 units in the Y axis and 6 in the Z axis.
Open the Attribute Editor for the new camera, and open the Environment section. Click on the Create button next to Image Plane. The Attribute Editor window will now switch to the Attribute Editor for the Image Plane.
Open the Placement section and click on Fit to Resolution Gate. This will ensure that your image plane will fill the entire rendered scene.
STEP TWO
While you are still in the Attribute Editor for the Image Plane, Click on the Map button next to Texture and map an envSky.
The envSky node is located in the Environment Textures section of the Create Render Node window.
STEP THREE
You will now set the colors for your environment. In the Attribute Editor for the envSky, Set the following attributes:
Sun Brightness to 1, 1, 0.5
Halo Brightness to 0.35, 0.36, 0.5
Under Atmospheric Settings, Set the Sky Brightness to 0.56, 0.617, 1.0
To change any of the color values, select the color icon next to the attribute. This will open the Color Chooser. Make sure you are using the RGB values by checking the RGB box near the bottom of the window. You can then type the values in manually.
NOTE: To open the Attribute Editor for the envSky, select the 3D Icon for the envSky texture and open the Attribute Editor. Click the Goto Output Selection Button at the top right side. This will take you to the envSky Attribute Editor.
STEP FOUR
Open the Floor Attributes section for the envSky, Map the color of the floor to a 2D Fractal texture.
Change the Color Gain to a Dark Green and the Color Offset to a Dark Brown. This will be your floor.
Select Camera 1 and Select > Panels > Look Through Selected. Turn on the Resolution Gate by selecting View > Camera Settings > Resolution Gate.
Render this view by selecting Render > Render into New Window.
STEP FIVE
When you render with the floor turned on, you may encounter a bright red surface for part of the floor. This is due to the fact that your camera is rendering a point that is below the Floor Altitude. You can fix this by either lowering the Floor Altitude, raising the look at point of the camera, or scaling the 3D icon. In this case we are going to scale the icon.
Select the envSky icon in the perspective view window. In the Channel Box set the Scale X Y Z to 5.
Re-Render your scene. You should now have a floor that extends to a vanishing point.
STEP SIX
You are now ready to add clouds to the scene. Open the Cloud Attributes section in the Attribute Editor for the envSky. Click the box next to Use Texture to turn it on.
Click the Map button next to Cloud Texture. This will open the Create Render Node window. Select a Cloud Texture.
STEP SEVEN
Preview your sky by rendering the Camera 1 view.
You will notice clouds in the scene but they are faint. You can make them more pronounced by setting the density. Set the Density under the Cloud Attribute of the envSky to 2.0.
Render your scene. You should now see clouds in the sky.
STEP EIGHT
Switch to your persp camera. If you take a close look at the 3D icon for the envSky, you will notice that there is a point that represents the sun. By adjusting the Elevation, Azimuth and Size, you will change the position and size of this point.
Set the Elevation to 90 degrees. This will position the sun directly in the middle of the sky and also produce the brightest light. Notice on the 3D icon, that the sun icon has moved directly to the top middle of your icon.
Render the scene. You should now see a bright blue sky.
STEP NINE
You will now position the sun so that it appears in your scene. To do this you will need to align the line that represents the sun to intersect a point in your image plane. Make the following changes to position and size of the sun so that it will be seen in the image plane.
Elevation to 10
Azimuth to 0
Size to 3.0
If you imagine the line on the 3D icon representing the sun going off to infinity, it will intersect the image plane which in turn will render the sun in your image. You may need to switch to your persp view and zoom out to see this.
Render the Scene. Notice how the color of the sky changes in relation to the elevation of the sun. At an elevation of 90, you get an image that has the brightest possible sky. At a lower elevation your sky begins to change to a darker color. However the appearance of the sun does not seem quite bright enough. In this case we will increase the total brightness to get a nice sunset.
Increase the Total Brightness to 3.0.
Render the Scene. You should now have a decent looking sunset.
Save your File.
CONCLUSION
You have now setup an envSky texture that will produce an environment complete with sun and clouds. There are many attributes to experiment with on this texture. You can achieve some interesting results by adjusting the some of the Atmospheric and Cloud attributes.