You can setup the database now if you want, takes about 20 seconds, just make up two words and one password and it's done, will then give you a username a database name a database host name and your password that you'll need to install Joomla.
To install Joomla, download the zip file, unzip it somewhere on your pc, everything that you've unzipped then needs to be uploaded to public_html, go to your website and you will see the welcome screen from Joomla asking for the database details, enter and you'll be inside Joomla (backend/admin area)
It will come fully featured with everything you need, you can change themes by going to sites such as
http://www.joomla-themes.co.uk/
As I say though, Drupal is easier for newcomers and very similar, here's a drupal site
http://www.rdamsenieuwe.nl/