Do you know what kind of home ponies love? Find out by designing one and seeing if the pony likes it!
Click on the categories in the top-right corner to see your options. Place the things you want to use on the blue dots. (You can move things around as much as you want, until you get them just right.) To delete something, click on it, then click the X in the bottom-left corner.
When you're ready, click the pony in the bottom left corner, and watch what happens. To get an official judgment, click Result.