In this tutorial I'll be teaching some basic techniques to light your scene using Maya software (default render-er).
Lights



In this part of the two part series, we'll be discussing the simplest light in Maya. The directional light is a great light for providing a 3d scene with a light source that comes as a ray (what I mean by this is if you rotate a directional light so it's shining at a 90 degree angle it'll shine light going in one direction for an infinity.). Since this is a basic tutorial, we won't be covering the in-depth details of the directional light. We're going to create a directional light. One way you can do this is by finding the directional light icon on the shelf or by going to create>light>directional light. Now, with the light selected, open the attributes editor. Go to window>attributes editor. The main attributes are color and intensity. You can find the shadow attributes under shadows. We'll be discussing shadows in part two.
Creating A Simple Under-water Lighting



Download and save the fish file. Now import the fish into Maya (in case you don't already know how to do this, after you've downloaded and saved the file, open Maya and go to file>import... Locate where you've saved the file and hit import.).

In this tutorial I'm assuming that you have watched the learning movies that come with Maya (help>learning movies). Create a directional light using the steps above, rotate and move it so it is sitting on top of the fish shining down. Open the attributes editor(window>attributes editor) and set the intensity to .8 and set the color to blue (when we reference a color, it doesn't have to be the exact color seen in the tutorial. This is just a personal preference. But since this is an underwater tutorial, it should be some type of blue.). [You must be registered and logged in to see this image.]

Create another directional light. This time rotate it so it's coming from underneath the fish, shining up at it. This is so we can mimic the light from the sun reflecting off the ocean floor. Reopen the attributes editor, set the intensity to .4 and set the color to a lighter blue than the blue you used on the overhead light. [You must be registered and logged in to see this image.]

Let's render our scene. You can click the screen icon or go to the rendering shelf and click it from there . [You must be registered and logged in to see this image.]

Our fish looks like it's under water, but it's got a black background. Let's change that. Go to window>outliner. In the outliner, select persp (that's the camera that we're looking through when we render). Open the attributes editor, roll down the attributes till you find environment tab. Set the background color to a blue. [You must be registered and logged in to see this image.]

Now let's make the water look foggy. Go to create>volume primitive>cube. Select it and open the attributes editor. On the top of the attributes editor, in the tab cubeFog, set the color to a light blue. Now scale it so it fills up the scene. [You must be registered and logged in to see this image.]

Render the scene. You should see a nicely rendered fish under water.
re-cap



Hopefully in this tutorial I've taught you the bare basics of lighting. In part two we'll cover more advanced]