I love flower gardens but I don't have a green thumb. I really don't have any know how on where to even begin

I have managed to plant 3 miniture rose bushes but I am amazed that they are still living because I haven't taken good care of them. I have two nice areas to plant flowers but there are a lot of small rocks in there. That I think is what is really stopping me. I have a lot of health issues and it is hard for me to get down and pick all those rocks out. I just love petunias, tulips and lilies but until I can tackle this I will never have a garden. I know it is too late this year, can anyone tell me where I begin and how to do it? I want you to know I appreciate your answers in advance.