It is a script that generates a minimap-ready texture out of your terrain.
The only thing you need to do is drop the TTMM script onto any terrain, setup a desired output resolution and hit Generate! That's really all you need to do. Textures are saved in the root folder of your project.
If you want your texture do display an ocean you can do so by enabling the 'use ocean' option in the inspector. When enabling ocean, make sure to select any non-transparent color for your ocean. This also enables you to change the color via any image editing software very easily.