In short you can earn money by writing hubs. The more traffic your hubs get the more likely it is that you will earn a profit. Now, I think it is important to note that you will most likely not make enough money to quit your day job.
You can get really fancy and add in links to products on Amazon.com and depending on if people click them or buy the products you could earn a little extra.
I think most people are on this site as a hobby with an added bonus of a little extra income.