Consider your expertise. If you take the time to reflect on your experiences, you will realize that you have more knowledge about which to write than you might think. Begin by listing three assets that define you, such as your profession, a special hobby or a personality trait. Next, list three things that inspire you, such as religion, education or charity. Finally, list three of your dreams, such as getting married, traveling or spending more time with your children. These three lists should give you many ideas of topics about which you can write.
You can sell your ebooks through Amazon's Kindle program or Apple's iTunes Connect, which gives you access to a large majority of the digital-book reading market and the barriers for entry are incredibly low. You don't need to invest lots of money to make this happen, but you do need to invest lots of time, not only in writing the ebooks, but in marketing them as well.
Now you’ve got many different options to start earning online. If you saw something that really interests you, try it out and learn more about it. If you’re really wanting to make a full-time income online, you need to be dedicated to learning how to do what you want to do. There are tons of free resources out there. You just have to search for them!
As someone who's been immersed in a number of online industries for quite some time, I know a thing or two about what it takes to succeed in this arena. However, just like you, I started at ground zero with little knowledge, but a great deal of passion. What I learned along the way were some invaluable lessons from failure that hurt at the time, but helped immensely in the grand scheme of things.