How do I start my underwater scene using Cycles?

I just want to start working on an under the ocean scene while someone else continue my desert scene.

Can someone provide an Step by Step tutorial?

I need to do it with Cycles because the internal render engine is aging and will soon die. Cycles is faster and just more realistic.It is the way to go.

All I need is a tutorial. Just a little bit is enough long as it pinpoints all the important settings I should adjust i.e. lightning, AO and volume lights, to have a good start.

A downloadable tutorial video should help as long as they are using Cycles engine.