After you've installed your packages, you have to 'mount' them in order to make them appear on your website.
Make sure you are logged in, and then click on the 'Admin' or 'Control Panel' link to get to the Site-Wide Administration page (at /acs-admin). Click on the subsite you'd like the application to be available at.
Subsites are a way of dividing your website into logical chunks. Often they represent different groups of users, or parts of an organization.
Now click on 'Applications' (applications are the same thing as packages). You'll see a list of Applications and the URLs that each is located at. To mount a new application, you click on 'Add application', enter the Application, title (application name), and URL (URL folder name), and you're done.
Test it out now. The URL is based on a combination of the subsite URL and the application URL. So if you installed a package in the Main Subsite at the URL calendar, it will be available at http://www.yoursite.com/calendar. If you installed it at a subsite that has a URL intranet, then it would be located at http://www.yoursite.com/intranet/calendar.