Hello,
After the stack is created, you can see the slot number is changed for the slave from 0 to 1.
[SW1] dis stac
Stack mode: Service-port
Stack topology type: Link
Stack system MAC: .....
MAC switch delay time: 10 min
Stack reserved VLAN: 4093
Slot of the active management port: --
Slot Role MAC Address Priority Device Type
-------------------------------------------------------------
0 Master ..... 100 S6730-S24X6Q
1 Standby ..... 100 S6730-S24X6Q
So the interfaces will change the slot in their name, from 0/0/1 to 1/0/1. First number is the slot ID, which is 0 for the Master(0/0/1 - 0/0/48) and 1 for the Slave(1/0/1 - 1/0/48). The stack features doubles the number of ports of a switch basically so they need to have different names to differentiate them.
Hope it's clear the process.