The CDN nodes store the data when it is first downloaded from the main server. The users can then access the data from the CDN nodes rather than the main server. Caching is at the heart of content delivery network (CDN) services. Similar to how browser caching stores files on a hard drive, where they can be more rapidly accessed, a CDN moves your website content to powerful proxy servers optimized for accelerated content distribution.
The following diagram can help you understand better how CDN Cache works
