Qualifications
This one's a doozy. You'll start off with a bachelor's degree. It doesn't have to be in a specific subject, but you better take some courses in biology, chemistry, physics, and math. And that's just the beginning. The next step is medical school. If you think getting into an undergraduate program is hard, wait until you see those medical school numbers. It's like an intellectual Olympics.
Once you get into medical school you need to take and pass all of the exams. This is no small feat—there's an awful lot to know about the human body, and almost none of the names of body parts, diseases, or medications come with easy mnemonic devices.
After all the studying and test-taking, you'll need to put that knowledge to work for a few years in a residency program. Finally, once all that is finished, you can qualify for a license to practice medicine (source).
But wait, there's more. You're not a urologist yet until you become certified by the American Board of Urology. Then, and only then, can you become a urologist.