Well I think is pretty clear in the instructions...
http://cmsrealty.org/index.php?view=items&cid=1%3Ainstall-cms-realty-20&id=1%3Ahow-do-i-install-cms-realty-20&option=com_quickfaq&Itemid=59Install Open Realty? in a subfolder of your Joomla install ( if your site is loaded on
www.yoursite.com then you would install to
www.yoursite.com/openrealty , for instance. Usually done by creating a directory in your Public_html directory name openrealty.
The one thing is not really clear is this one
# If you haven't already, rename the htaccess.txt file in your Joomla root folder to .htaccess.
# Modify your .htaccess file
* After the line with 'RewriteEngine On' add the following (replace XYZ with the item id you want to use for the links):
######Changes for OR Notification links######
RewriteCond %{QUERY_STRING} ^.*listingview.*$
RewriteRule ^listings/index.php(.*) index.php?%{QUERY_STRING}&option=com_cmsrealty&cmsrealty=user&Itemid=XYZ [R=301,NC,QSA,L]
######Changes for OR Notification links######
that one, no idea..