Your site is called a Portal, you could potentially have different portals in the same DNN installation, these would be completely separate sites.  That's why it's not just a simple "your website."

When you installed the site, you should have setup a username and password for the host account and the admin account.  The host is over all portals, the admin just have access to your first portal.  If you login to your site using that host account, there will be two additional items in your menu, Admin and Host.  Under the Host menu, you can go to the Module Definitions page.  This shows all of the modules that you have installed on your site.  Using the action menu in the upper left corner of the module, you should be able to select the option to Install a New Module.  You will be able to upload the Inventua package here, and it will install on your site.

Hope that helps,

Most packages aren't meant to be opened in Visual Studio (or VWD).  They're used, setup, and administered through the DNN site.  When you're logged into your site with administrative privileges, there's a control panel at the top of the site.  In the middle of the control panel, there's a drop down list of available modules.  If you choose this Inventua module from the list and add it to the page, you should be able to set it up from there.

Hope it helps,