Countries that choose to incentivize their citizens' private commercial undertakings quickly see their efforts rewarded. Not only do more citizens rise to the status of Great Merchants, but their famous trading trips start producing much more wealth, both for themselves and for your empire! Thus entrepreneurship turns into the base for the most advanced undertakings of economic expansion.
This is one of a series of Policies which aim at boosting the main types of Great People. The effect is self-explanatory, but keep in mind that you still need to produce the Great Person Points for a Great Merchant (usually via Merchant specialists in cities) in order to use the 25% bonus. Also, you won't benefit from the double Gold bonus if you use your Great Merchants to build Customs Houses instead of traveling and doing trade missions in city-states. Note that Influence points gained by trade missions remain the same - it is only the Gold bonus that increases to a whopping value!
So, after adopting this Policy try to maximize your Great People generation via any means necessary (including adopting the Sciences Funding resolution in the World Congress), and then get ready to send out your Great Merchants on as many missions as possible. And then plan on what to spend the tons of Gold you get! This will depend on many factors, such as victory strategy and momentary needs, so we will not discuss them here.
Entrepreneurship, from the French term "to undertake," refers to the capability and willingness by an individual to develop, organize and manage a commercial venture in the hopes of making a profit. In history, entrepreneurship has taken many forms, from the great explorer-merchants of Renaissance Italy to the government-chartered companies of the Age of Discovery to the robber barons of the Industrial Age; regardless of the form, the willingness to risk their own funds to generate greater wealth has driven the evolution of civilization as surely as any other factor.