Input groups are extended Form Controls. You can easily prepend and append text or buttons to the text-based inputs with the help of input groups. Also, you can add common elements to the user’s input. For example, you can add the dollar symbol, the @ for a Twitter username, or anything else that might be common for your application interface.
To prepend or append elements to a .form-control you need to do the following:
Wrap it in a
with class .input-group
In the next step, place your extra content inside a with class .input-group-addon.
Now place this either before or after the element.