Start by drawing a rectangle with the Rounded Rectangle Tool. You can use the Pathfinder Palette to make a traditional matte or the more simple technique is to give your rectangle a really thick stroke. Place your rectangle on it's own layer and keep all other layers below it. As we continue throughout the tutorial you can make new layers as you see fit to place your different objects on. We will leave that up to your discretion; as such, we won't be pointing out when we make new layers.
In lieu of making a matte that covers the square edges of your artwork, you can again use the Pathfinder Palette to trim any of the art that touches the corners of the rectangle. This is more time-consuming and mainly useful when your final artwork should not contain any additional objects, like a matte.
Draw a rectangle and give it a nice greenish-blue color. This is the basis of what will become the sky. Note that this looks like a rounded corner rectangle because it is behind the matte layer.
