What you're going to do is look for a purple swirly remix button that says "Remix" on it. Then, you're going to go into the costume/backdrop editor (whichever one it's in) and design your horse! You can add colors, accesories, tack, and your name typed under it! Finally, you go up into the corner with the project name on it and press save-->publish.
I love horses and I'm glad I can share my joy!!!