Question

How to Redirect Non-www to www URLs using htaccess ?

Answer 1

You need to add 

RewriteCond %{HTTP_HOST} !^www.example.com$ [NC]
RewriteRule ^(.*)$ http://www.example.com/$1 [L,R=301]

in .htaccess file. Note that you must put the above lines somewhere after RewriteEngine On line.