The Constitution does not say anything about Congress having the right to make laws about things like minimum wages or maximum hours that workers can be asked to work. Therefore, if Congress can make such a law, it must be because of its implied powers.
In this case, the power is implied by the commerce clause. This is the clause in the Constitution that says that Congress can regulate interstate commerce. This implies that Congress can regulate things like the wages and the hours of people who work in businesses that are part of interstate commerce.
In this way, the FLSA comes from powers implied in the commerce clause.