Your website can bee seen as a slightly different number of different URL's.
http://weseo.com.au
http://www.weseo.com.au
Having multiple locations of where a search engine can find your homepage, can lead to a penalty. Having a canonicalisation URL means that you have only one location where your web page is possibly found. By setting up your website properly you can redirect visitors and search engines, who view other versions of your web page. This is achieved in the .htaccess file located in your website root directory.
.htaccess example to avoid canonicalisation
< IfModule mod_rewrite.c>
RewriteEngine on
# index.php to /
RewriteCond %{THE_REQUEST} ^GET\ /.*/index\.(php|html)\ HTTP
RewriteRule (.*)index\.(php|html)$ /$1 [R=301,L]
# force www.
rewritecond %{HTTP_HOST} ^weseo.com.au/ [nc]
rewriterule ^(.*)$ http://www.weseo.com.au//$1 [r=301,nc]