Webhooks in Subgraph work by sending real-time data results via HTTP Post requests for all the entities in which you have enabled webhooks. So, if a subgraph handler executes a call method like entity.save(), an update is reflected to the intermediate database powering the underlying subgraph API. A real-time watcher then interprets this update and puts it to the webhook handler while enabling a few important operations like UPDATE, INSERT, or DELETE. A Subgraph can store different versions of entities with their block_range column, enabling you to understand the difference between the true entity change or changes occurring due to the reorganization of the blockchain.