Why are IDs showing in URLs when clean URLs are enabled?
The Clean URLs setting turns your URLs from index.php?q=node/123 to /node/123.

The path module that comes with core Drupal enables the URL path settings tab on node add/edit forms. Here you can specify any URL alias that will load the node instead of /node/123. These aliases must be entered manually for each node.

The Pathauto module allows you to automatically generate URL aliases. By enabling pathauto and not doing any further configuration your URLs will turn into /content/title-of-node. You can change how the URL is generated in the pathauto settings (so it can be /node/title-of-node for example).