What do you have to work with? Can you share any photos?
Start with deciding do you want annuals or perennials.
Determine your zone.
Analyze your soil.
How much work do you want to put into it?
Then use these factors to research and plant your garden.
Space, temperature, and soil type will help determine what you should plant along with a sun/shade areas. Of course find what planting zone you are in is another major factor. Your local nursery should have the knowledge of what you can grow successfully and can provide you with a good variety of plants that will do welll where you are. Where you choose to locate your flower garden is up to you and how to arrange it. Bet it willl be beautiful!
Raised beds are a wonderful way to grow most anything - even flowers. Check out this site for fabulous ideas, inspiration, and a TON of information: https://www.gardenupgreen.com/2018/03/four-raised-bed-garden-ideas.html