db_query or db_select for getting content type fields
If you have your node object, you can use field_get_items to get the field values from the node.

$items = field_get_items( 'node', $node, 'field_name' );
// now $items is an array of values... you can manipulate...
// then use the field_view_value to build the render array
$specific_item = $items[0];
$item_build = field_view_value( 'node', $node, 'field_name', $specific_item );


Here's a link to the field_view_value API doc.

Use the devel module and sprinkle in some dpm()'s to understand the underlying data. It's pretty neat! :)