Drupal itself provide good caching options to increase the page speed and serve pages fast to end users. Caches are used to improve the performance of your Drupal site. But it also has a drawback that sometimes it could lead the "stale" data. This means, sometimes, the system may start to serve the old pages from the cache.

How to enable Drupal site and block cache on various Drupal versions? See below for answers: Drupal 6:

1. Go to Administer -> Site Configuration -> Performance.
2. Turn on cache options
3. Enable the JS/CSS files aggregation and save it.

Drupal 7:

1. Go to Administer -> Config -> Development -> Performance.
2. Turn on cache options
3. Enable the JS/CSS files aggregation and save it.