How are the terms free market free enterprise and capitalism related?

It depends on how one defines "capitalism." For many, capitalism is just another Word for a market-oriented economy. But there are many usages, which may lead to confusion.

If one is considering it as a matter of the importance of capital and investment, they are linked because of the nature of the market. Because entreprenuers may not have the resources to start a business, or may need to establish themselves before they become profitable, outside capital becomes imperative. Outside "capitalists" offer capital to those firms they believe will be successful, i.e. provide a meaningful service at profit, in the future. The cycle of renewal and competition in a marketplace thus relies heavily on this sort of capitalism.

Or if you define it in class warfare terms, where capitalism is the system benefiting the wealthy, the matter of price of labor in a marketplace becomes important. Wages, like all other prices, are a matter of supply and demand. Some people, like entreprenuers, athletes, and entertainers, provide services that are in high demand, but for which there are few able to fill the role. As a result, the market awards them greater profits, thus the "capitalist class" is created.