Flower gardens are for enjoyment. They provide you with visual beauty, the joy of working with soil and plants, and the pride of showing others what you have created. As a gardener, one is always experimenting and learning anew what delights a flower garden may bring forth. This enjoyment can be intensified by creating your garden, or a room within the garden, with a theme.
Think of the old formal gardens with their hedges uniquely designed to provide a visual appeal that has survived the ages. Think of the Japanese Garden with its calm Zen-like quality. Theme gardens can be based upon a historical time or place or special types or colors of plants. They can be created for the wild creatures we hope to draw to our garden such as butterflies or hummingbirds.
Each type of garden has an unique appeal and some even more pleasing gardens can be had by using combinations. We Americans are famous for being the "Melting Pot", for combining things we have brought from the rest of the world. Imagine having a butterfly garden surrounded by old rose varieties. Imagine a vegetable garden with a Zen garden in the middle. The combinations are endless.
The book Theme Gardens by Barbara Damrosch is a great starting place. She has several types of theme gardens with pictures and layouts. Use these plans to create your own just like her suggestions. Or lay out a garden that is uniquely yours using these plans as a starting point. There is no real right or wrong way to lay your garden out, so learn as you go and have fun.