Input groups are extended Form Controls. Using input groups you can easily prepend and append text or buttons to the text-based inputs.
By adding prepended and appended content to an input field, 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 -
Wrap it in a <div> with class .input-group
As a next step, within that same <div> , place your extra content inside a <span> with class .input-group-addon.
Now place this <span> either before or after the <input> element.