Typography - Font Awesome - change icon

I know that typography icons is a kind of font type, but I need two not found icons, a Bike and an Animal. Question: Is it possible to change the icon from one existent class? or Is it hard to create my own class with my own icon and use it in the same way that we use "icons font awesome"?

thanks

Are your new icons inside font awesome?

No, I don't know how I'll put my own icons on this font. I did not even know this was possible. How?

What You need to search for is an information about css sprites.
While your request is more general than specific that is as much as I can help.