To commercialize something is to make money from it. If you're a painter, you might commercialize your art by printing greeting cards and selling them online.
The verb commercialize comes from the adjective commercial, "done for financial profit," and its root, the Latin commercium, "trade." When you take an activity or an organization and manage it so that it results in a profit, you commercialize it. Delivering baked goods to your neighbors out of a sense of generosity is one thing — when you start charging them two dollars per cookie, you've commercialized your hobby.