how to create an ocean in unity3d?

Please be more specific, especially for guys like me that a) haven't played the game and b) have little chance to find out what game you talk about (seeing how generic the title seems to be) and what ocean in that game you mean (given that it might be a game with like 10 different oceans in it, each created in a slightly different way).

- Best thing is to show an image that shows the ocean clearly

- Second best thing is to accuratly describe how the ocean looks

I am working under the assumption you are only talking about graphics here, right? I am also working under the assumption you are trying to create a photorealistic effect. Then, seeing you say the Unity standart ocean shader cannot do it, I guess you are either specifically talking about:

1. Foam on waves and shore

2. real wave displacement, either by using a mesh or tesselation

3. underwater caustics

IF you have a budget, have a look at the asset store. There are too many ocean shaders and systems in it to count, some of these looked really high-end.

Almost all of them are not cheap, at least not for a Unity asset store asset (seeing how much dev time it could save you, however...)

For all of these effects you will find tutorials with some google fu. They might not be for Unity, Shaderlab, or even C#, so you might need to translate between languages or from pseudocode to shaderlab / C#.

But if you are looking for phototrealistic oceans for free in Unity, you will have to do some work... scratch that, a lot of it.

Other engines might have much higher end water systems already built in, so maybe check them out first. Maybe Unreal Engine 4? Don't know for sure.

here are two screenshots to hopefully help greaten the ability to understand what OP is asking for. :)

I see a water plane plus some wave vfx.

The water plane is simple enough: plane plus a shader. The complexity of the shader and the resolution of your water plane is something to negotiate and is up to you and your graphics card.

The wave VFX I can see don't look like they deform the plane, they just modify the lighting and textures to look like white caps.

Perhaps make a plane and add a shader, as suggested by Frob?