Drupal Api site gives only a quick description of avaliable functions. In most cases there's no examples of usage. save_node function is so important that I have to give a working example with CCK fields. Here it is:

Here is saving new node:

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

// add CCK field data
$newNode->field_{YOUR_CUSTOM_FIELD_1}[0]['value'] = '{DATA_1}';
$newNode->field_{YOUR_CUSTOM_FIELD_2}[0]['value'] = '{DATA_2}';

// save node
node_save($newNode);

?>

And here we have update of node title:

<?php

$update_node = node_load($nid);
$update_node->title = 'update title';
node_save($update_node);

?>

That's it :)