Do you have to be half decent from the start? How do you improve your singing voice?
If you are tone deaf, vocal training won't do you a bit of good. However, vocal training will help you improve you voice regardless of your "talent" level. Vocal training just means that an instructor teaches you techniques to control (such as breathing correctly) your voice and expand your vocal range. I've taught children and have taken at the college level. It's like piano lessons for your voice.