An infographic is simply a visual representation of data and information. Well made infographics often take complex sets of data and boil them down into something that is easy to understand. Many companies and news organizations use them to create compelling stories for their customers and audiences. While many of these organizations hire professionals to create these graphics, there are many websites that allow you to create your own for free.
Every free infographic Website has it's own visual aesthetic. It's a good idea to look around a bit and see which style best matches the story that you want to tell. There are many more than these three, but this should give you an idea of what kind of things you can do with these tools.