Venture capital is a sub category of private equity. All venture capital is private equity, but not all private equity is venture capital.
Venture capital is good for new companies with little or no history that cannot raise capital in the public market and cannot secure a bank loan or a legitimate debt offering. In exchange for a high risk venture investors assume by investing in smaller companies, venture capitalists usually have control over the company decisions, and a significant portion of the company's ownership.
There are entrepreneurs who have ideas but lack the capital for an initial investment. Venture capital facilitates the start up phase of a new company.
Venture capital funds have a fixed life of 10 years. Extensions allow for private companies needing liquidity.