Some tips and tricks behind accessing information from the Joomla database:

• Accessing the current user object - an article on how to display user information. Using the following code, you can obtain registered user information:
  $user = JFactory::getUser();
  echo "Your name is {$user->name}, your email is {$user->email}, and your username is {$user->username};
  echo "Your usertype is {$user->usertype}";
  
  There is also a very good plugin, Bixie Userinfo Displayer, that can be easily used in any Joomla article, such as Guest for the users full name.
  
  
• Selecting data using JDatabase - an article on how to access information from any Joomla table, using JFactory::getDbo();