An ocean is defined by a flat surface with an ocean shader assigned to it. Fluid Effects simplifies the process of creating an ocean by providing a single command that creates a plane that is optimized for best results and an ocean shader, with appropriate connections.
The ocean plane is a NURBS plane with more detail concentrated in the center so you can have the ocean extend to the horizon, but see a reasonable resolution locally.
Since interactive shading would slow down playback, the shading is turned off for the surface. You need a preview plane to see displacement and shading in hardware display.