There are two main ways to increase the share capital of a corporation: either by issuing new shares, which will raise fresh capital for the corporation, or existing shareholders can transfer or sell their shares to another purchaser.
Angel investors are high net worth individuals who choose to invest their personal funds in a start up in the hopes of a healthy return on their investment. Angel investors are typically there as sources of money for purposes of growth and scale of early stage businesses, not as advisers that act in the role of management, although this is possible if the owners request it.
Venture capitalists are comprised of a group of professional investors. Their capital will come from high net worth individuals, corporations, endowments, insurance companies, pension funds and foundations. Venture capitalists are willing to risk investing in such companies because they can earn a massive return on their investments if these companies are a success. VCs experience high rates of failure due to the uncertainty that is involved with new and unproven companies.
