All Drupal contents are base on node. Whatever contents you create, it has a url http://<drupal_root>/node/<node_id>. For each content, you can customized the URL alias but think about if you have 100 nodes, you will not enjoy setting the each alias manually. It’s better to pass the job to PathAuto.
After installation, go to @ Administer –> Site building –> URL aliases. There is a new tab called Automated alias settings. For every Story content type, i want the URL alias to be http://<drupal_root>/stories/<story_title> so i set stories/[title-raw] in Pattern for all Story paths.
Reference: Drupal Module – Pathauto