Sooner or later everyone has to make use of some kind of caching of their content. Below is the simplest possible code demonstration on how to implement caching with Cache_Lite (download Cache_Lite standalone PHP class file which you can just include to your project without having to install it through PEAR):

require_once('Cache_Lite.php');
$cache = new Cache_Lite(	
  array(
    'cacheDir' => "cache/",
    'lifeTime' => 20 //seconds
  )
);

$req = "file.txt";
if($data = $cache->get($req)) {
  echo "Result from cache: " . $data;
}
else {
  $data = file_get_contents($req); // this is usually a DB call!
  $cache->save($data);
  echo "Result not from cache: " . $data;
}

So, first you require the class file, make a new instance by setting a caching directory and cache lifetime. For demonstration purposes I'm outputing the contents of file.txt but of course in a real use case scenario that would be some result of a database query or sth like that.

Simply, to get the data from cache (if it exists) you have to call the get() function on the Cache_Lite object, and to save it, well, use save() function and you're all done.