Recently I was working on a project where I was carrying out some additional page queries and therefore using the excellent WP_Query class with WordPress. The requirements were slightly different however as there was some custom sorting needed. Here is how I utilised sorting the results of WP_Query with multiple post meta keys.
WP_Query is the heart of a more complex WordPress site build as it allows you to query different content objects in WordPress and then loop through the results to display these in your templates where you need to. Rarely do I build a site without it.