OK HOW DO U MAKE A 바탕화면 IN PAINT.NET?, IF U HELP ME U WILL GET A PROP

Paint.NET is probably not the best program to be using if 당신 want to create a professional-looking wallpaper. Can I suggest GIMP?
And, as for "making pictures look like they came together", I think you'd use the smudge tool to make the edges blend together. I'm pretty Paint.NET doesn't have this feature.