VirtueMart is an Open Source shopping cart application specifically written for Joomla!. This means, that you cannot use it unless you also use Joomla!. Both, Joomla! and VirtueMart have a huge international user and developer base. Below are documentation links to help you use your VirtueMart shopping cart to its full potential.
Please note: VirtueMart 3.x is now available for Joomla 3.x