How would I go about it?
Is there certain training I need?
Could I design dresses but hire someone to make them?
Would like as much info as possible please
yes. you can design your own dresses and hire someone to make them. if you are a wedding dress designer and have talent, just put up a website and buy advertizing on as many of the websites which list wedding gown designers and vendors as you can afford. it is expensive, but that is about the only way other than word of mouth if you want an online business.
or you can hang a sign on your front door and advertize locally to try to get some business. once you have your first customer, they will help you by telling others.