If you have used Magento for any length of time you will know about the Cache.. but for those new to the platform….
To speed up the serving of pages to your websites viewers Magneto heavily caches content.
This is great as it means quicker page loads, lower strain on your hosting resources BUT it also means that changed made in the admin (or at a code level) may not display or update on the front end view of the website.
So during development turn off the cache, and on a live site turn it on but be aware of this when installing any extensions or making changes.
Also beware that the cache can become very large over time, along with visitors logs held in the Datebase. So best practice is to have a clean up script running weekly / daily (as needed) to clear down the logs and remove the cached files.