You can use leftover materials to make something like this. You'll need full sun and well-drained soil. An elevated sight is recommended so these little beauties aren't lost among taller perennials. You don't have to have rocks, but they can certainly add interest to your garden. Don't forget foliage, either.
Foliage is what ties any garden together.
Greenery adds texture and helps keep your garden interesting, even if nothing at all is in bloom. You can learn more about rock gardening plants by visiting public rock gardens. Allen Centennial Gardens on the UW-Madison campus has a superb rock garden. It will give you lots of ideas. They're open to the public from dawn to dusk, year round.