please complete your profile here in IDEA so that we can see what you already have. The profile here is also a good way to get your name ‘out there’ so that people can find you if they use IDEA to search for a personal trainer.
Whether you need to set up a business depends on where you intend to train. If you were to become an employee at a gym, you only need (hopefully) a personal trainer certification, and the gym takes care of all the rest, including your liability insurance.
If you want to become independent, then you will need to set up a business and will need to get your own liability insurance. Information about setting up a business are easy to fin. Here is a link http://startfitnessbusiness.com/how-to-start-a-personal-trainer-business….