This is a simple Photoshop Tutorial, by using few methods and brushes you can simply create a Beautiful wallpaper. Your final image can be like this...
Choose #4986FB color by clicking in the "set foreground color" in the tool box. Its sky blue color, you can choose any other color if you don't like this. Click on the "Gradient Tool" or press "G" to select this tool and draw a gradient as below.
Then draw structure or mound as below
Then we have to grow some grass on it to make it eatable for animals. :D
Select grass brush and grow some grass as below
Then open Nature Brush and draw a tree on suitable place, i used this brush as below
Now lets go to the last step, create few humans standing on the grass, you can use Human Brush for this. Now your image is as below
Now you can put some clouds on this image. Copy clouds from wallpaper and past it on the layer we created in the first step. Set the layer "Blend Mode" to Lighten and your image will become like this.