To start I would just look for a basic and well maintained used road bike or hard tail mountain bike. Then get out and ride. As you ride more, you will get a better idea of what sort of riding you want to do and what gear you will need or want to do it.

Do you have a friend or family member who can help you pick a bike that is in good shape and will fit you? If not, keep trying shops until you find someone who is helpful. Good luck.