If you have a great business idea, or a great business which you want to excel with some extra cash, then you can pitch it to investors who are interested. If you have tried raising the investment money through other means, and haven't been successful, then this is a good way to secure an investment.
In the majority of cases, you will also have found a great mentor/guide for your business as well, who can help you excel your business idea because of their experience and knowledge. In return, the investor may ask you for a percentage share in your business. At this point, it is up to you and the investor to negotiate the deal down to its more finer points. Once both parties are satisfied, then a contract can be signed, and the investment money will be injected into the business.
In order to secure investment, the first step is to create a business plan. Once the business plan is created, the next step is to send your potential business investor/s the business plan. If the business plan appeals to the investor, then the investor will get back to you and then you can have further discussions or meetings regarding your idea/s.