Installing an SSL Certificate makes it possible to connect to your site using SSL over port 443 using https:// but does not automatically force the usage of SSL.

The example we often make is to think of installing SSL like adding an extra entrance to a building.  Simply adding an extra entrance does not automatically mean that the entrance is going to be used nor does the simple existence of the additional entrance mean that the old entrance is no longer there or usable.

It is possible to force the usage of SSL and how you go about it varies based upon your content.  Some software like WordPress generally you can simply update the Site URL within WordPress to reflect "https://" instead of "http://" and it will re-direct.  In some cases it will not auto-redirect and you'll still need to configure a manual re-direction.

For directions on re-directing non-SSL to SSL traffic automatically please see this article: How do I force SSL using .htaccess