To migrate content into Drupal nodes, use the MigrateDestinationNode class:
$node_options = MigrateDestinationNode::options($language, $text_format);
$this->destination = new MigrateDestinationNode('article', $node_options);
$arguments = MigrateTextFieldHandler::arguments(array('source_field' => 'source_teaser'));
The first argument is the bundle (content type) you wish to migrate source content into.
nid - The Drupal node ID. Usually this will be unmapped - the nid will be automatically assigned when the node is created, and the map table will record the source key that generated this ID. You will need to map the nid when the system-of-record is DESTINATION (i.e., the purpose of your migration is updating existing nodes rather than importing new nodes). Also, if you want to maintain the same content ID as you had in the source system, you would map that ID to the nid as well as setting the is_new option.
created - The date and time when the node was created. If no value is mapped from the source data, this will default to the time the node is imported by Migrate. Note that while this is ultimately stored as a UNIX timestamp, any absolute date/time string supported by strtotime() can be mapped to this (or generally any other timestamp field).
changed - The date and time when the node was last modified. See also created. Note that if not mapped, it will default to the time the node is imported by Migrate.
is_new (Drupal 7 only) - An option that, if set to TRUE, will create a new node using the value mapped to nid as its ID, rather than generated a new sequential ID. Because the Migrate module maintains the mappings of source to destination IDs, and supports automatically substituting them with sourceMigration to maintain relationships, this is rarely necessary (even if you might think you need it at first glance).
The language option will be applied as the default language for any node fields which are language-dependent. If unspecified, it will default to LANGUAGE_NONE.
The text format (e.g., 'filtered_html') will be applied as the default text format for any node fields which take a format. If unspecified, the default for the field will be applied. On Drupal 6, this should be set to the numeric text format value (i.e. '1' for Filtered HTML - see the filter_formats table to find the numeric ID) rather than the human readable name for the filter.
Support for the core Statistics module was added in v2.4. Map like any other node field.