Now it's time for an introduction to using Blender Paint. It takes a while to detail landscape realistically, so here you are going to use some broad brush strokes now just to get an idea of how Blender Paint works. It's good to go online and look at images of islands like the one you want to make, for ideas on how the soil should look, and what the plants and trees should look like. Using the satellite views of Google maps can give you ideas too:
Go down to the Timeline window below the 3D View window. Select the Current Editor Type button in the lower left-hand corner. Choose UV/Image Editor from the menu.
Move the mouse to the boundary between the UV/Image Editor window and the 3D View window. When you get the double arrowhead, move the boundary up so you can see the grid background in the UV/Image Editor. You can also use Ctrl+MMB to zoom out to see the whole grid.
If you see a rendered image in the UV/Image Editor window, delete it by pressing the...