How can I create some specific content with a cron job
You got it!  Implement hook_cron and inside that function create a node using the node_save().

Each time you run cron by going to /cron.php or each time it is called from your cron job, your hook will automatically be called.

Here's some sample code, partly borrowed from http://drupal.org/node/1111514

So your .module file should at least have the following,

// Implementation of hook_cron
mymodule_cron {

  // add node properties
  $newNode = (object) NULL;
  $newNode-&gt;type = '{NODE_TYPE}';
  $newNode-&gt;title = '{NODE_TITLE}'
  $newNode-&gt;uid = {USER_ID};
  $newNode-&gt;created = strtotime("now");
  $newNode-&gt;changed = strtotime("now");
  $newNode-&gt;status = 1;
  $newNode-&gt;comment = 0;
  $newNode-&gt;promote = 0;
  $newNode-&gt;moderate = 0;
  $newNode-&gt;sticky = 0;

  // add fields
  $newNode-&gt;field_{YOUR_CUSTOM_FIELD_1}[0]['value'] = '{DATA_1}';
  $newNode-&gt;field_{YOUR_CUSTOM_FIELD_2}[0]['value'] = '{DATA_2}';

  // save node
  node_save($newNode);
  }


After you enable your new module, just run cron by hand (go to /cron.php) and test it out to see if your node was created!