I'm a newbie to creating extensions and really wish some info was here, so I'll take a stab at adding what I figure out in hopes of helping others.
Access the JFactory using the php code:
$var = &JFactory::content();
Here are a few lines that are included in examples. They should each be explained.
$database = &JFactory::getDBO(); $document = &JFactory::getDocument();
$uri = & JFactory::getURI(); $id = $row->id;
The following provides access to the logged-in user info. Read more here... Accessing_the_current_user_object
$user =& JFactory::getUser();