There are two methods for content distribution in CDN: Origin Pull and Origin Push. Based on how you would like to place your content on CDNs edge servers, you can choose one of them.
In the Origin Pull method, after deploying CDN on your origin server, the first request for the content will be retrieved from your origin server. Then it is cached and served to the requester. Next requests for the same content will be served directly from CDN’s Edge servers. In this method, you don’t need to transfer your content to CDN’s edge servers.
In the Origin Push method, you need to transfer your content to CDN. The transfer can be done using different methods such as FTP. Then CDN distributes these contents to edge servers.