By default your website can be accessed with both www.example.com and example.com.
Since Google penalizes this due to duplicated content reasons, you should restrict the access to either www.example.com or example.com.
Some links may be outside of your website scope and/or the search engines may have already indexed your website under both addresses.
The htaccess redirects generator wants to facilitate the implementation of the most common redirects scenarios via htaccess, especially used when implementing SEO best practices & recommendations.
Just select the desired scenario and obtain a personalized code based on your input, ready to copy & paste.