If you have taken classes in cake decorating and design, and you have a talent for your creations, you might start offering your cake decorating and design service to your friends and neighbors.
Word of mouth will travel quickly, so make sure you know your stuff before taking any paying jobs! Much of your business will come from past customer referrals, and people who were at the event and saw your beautiful and original creation there.
You'll need adequate space in your home, along with the equipment you'll need.
It's a good idea to take photos of your finished designs in case a potential client wants to see your work.