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I would like to break this in stages of new business. In the first stage when a person has idea only, he has to take his own savings or partner with some close friend who believe in his idea and start the business.
Once the idea takes shape and it looks like real business you can identify potential business partners who have invested in similar business through online forums or business meetings. In this stage you have to prepare a "pitch", which is summary of your business idea, revenue forecast, competitor and market analysis. This is presented to venture capitalists or bankers who are ready to take risks and invest in new startups.
These investors get share in equity capital and provide guidance. Once the company take sizable proportion in terms of business model, revenue flow and stability you can go public. Remember facebook and twitter. All the best.