Everyone on this string is spot on. To really understand and get an answer to your question, you need to find someone who owns a company much like you are dreaming about. Ask them questions. Shadow them. If your dream is a big company that already exists, find some one who works there.
I also suggest reading books by entrepreneurs who started a business in a sector you are interested in. Reading their experiences will give you a sense of what it costs, the sweat equity (that's your personal time and passion) and how they did it. Good luck!
Jennifer recommends the following next steps:
- Find an entrepreneur to shadow and ask questions.
- There are many books on starting a company. Pick one up and start reading.