How the Storage area network (SAN) structure works?

SAN works based on HBA from server (wwn) zoned to storage array mapped to LUN

A storage-area network is typically assembled using three principle components: cabling, host bus adapters (HBAs) and switches. Each switch and storage system on the SAN must be interconnected and the physical interconnections must support bandwidth levels that can adequately handle peak data activities.

To start with :

SAN is to provide huge data storage space to servers using a separate /private network other than the regular Ethernet/management network. 

In SAN (storage area network), the pooled storage resources and the servers that access this storage are separated by a layer of management software. The software allows IT administrators to centralize and manage multiple storage resources as if it were one consolidated resource. Because of the software, each of the servers sees just one storage device, while each of the storage devices in the SAN sees just one server. Data can be moved at will to any of the devices on a SAN.