I collected information about terrain rendering on my notebook a while ago. You can find it at http://www.gamedevpensieve.com/graphics/3d/landscape .

Smkviper is wise...

Start with rendering a triangle.

Generate an isosphere. Give it an equirectangular uvmap. (You can download free planet textures to test it)

https://github.com/jeske/SimpleScene/blob/master/SimpleScene/Util/IcoSphereCreator.cs

Generate some random noise into an equirectangular "displacement map" texture. Use it to displace the isosphere verticies, possibly on the gpu.

Control the isosphere tesselation with a screen space size approximation. So parts of the isosphere close to the camera are subdivided more. Use caching, or gpu tesselation.

Replace the premade displacement map with a generation function, and generate pieces only when needed, at different levels of detail.

That should get you close..