The first step is authentication. You can use Google's own example detailed here which runs you through the entire procedure of doing that.

Once you have authentication complete, you can do the following: Register for an API key here.

<?php
// add node attributes
  $yourNode = new StdClass;
 
  //Set Node Type, as blog,page etc. 
  $yourNode->type = 'NODE TYPE';
         
  //set title of your node
  $yourNode->title = 'NODE_TITLE'
 
  //Set user or author of node, 1 for admin.
  $yourNode->uid = USER_ID;

  //Set node Status as published.
  $yourNode->status = 1;
 
  //Add node Body
  $yourNode->body = 'This is body Content';

    //add CCK field data