Font Awesome is an icon font pack. ie, images can be used as font characters. When we type " A " that is a drawing which represents " A ". The same way we can use images that represent something else. Once you tie it with Unicode or link it with HTML and CSS, the scope is very vast.
Font Awesome comes with 3 sets. Regular, Solid and Light. There is also Duo tone icons as shown above. The free version does not covers all of them. Duo tone icons are Pro version exclusive. Duo tones icons can also be painted in colours using
fa codes within your HTML document. They are a great example of awesome graphics and very smart code.
Hope you will enjoy using them in your projects. In short, if you want to use images in a very simple and flexible way while designing web pages ( and more ), you can use Font Awesome and its vast library.