Stack master is the core switch to manage other stack members and it stores the running configuration files for the whole switch stacking. basically after you have configured the stack, you can manage it as if it were a single device, as you can read form the document, both devices are responsible for traffic forwarding (Data Plane), but only the Master switch manages the control plane You can configure the stack as L2 or L3 device. Yes., the core connects to distribution layer and distribution connects to access layer switches. For switch to be in HA, we need to do stacking right or Hsrp might work but for cisco catalyst switch there is no hsrp. Stackable switches improve network scalability, reliability, and flexibility by increasing bandwidth and simplifying device management.