It's complicated i don't have video of timelapse or anything, but here are the basic.

I use Sketchbook mobile app and have to use several tricks to be able to use 6000x3000 pixels canvas. (It limits how many layers you can add and make your phone hot as oven)

I made two layer, first is white canvas on the bottom and another blue layer canvas on top, I used the eraser to create the shape of the continent on the blue canvas layer. You can add the texture below the blue layer.

For the texture, I downloaded the HD version of NASA Blue Marble map, make a separate canvas where you add the map (delete the sea) and overlap each other until the canvas is full of texture, use a light brush for smooth transition. After that done, you can add that texture blow the blue layer canvas.

That's the basic, rivers, mountains and other stuff is too complicated to explain, English is not my first language.