Hello Shivam
I am doing fantastic, thanks! I hope you are too! 
HSRP is always applied to a Layer 3 interface, and cannot be applied to a Layer 2 interface on a switch.
When we talk about routers, all configurations are applied to the physical interfaces themselves since they are always Layer 3 interfaces.
For multi-layer switches however, you can apply HSRP on a routed port, or on an SVI because both are Layer 3 ports.
Now the tricky part I think is, within a topology, how do you know which Layer 3 ports to apply the commands to? The key is this: The Layer 3 ports that will play the role of the redundant default gateways must be in the same subnet/network segment/broadcast domain.
So for two Multilayer switches that are connected to each other with a trunk, you would apply the HSRP configs on the SVIs of the same VLAN. If you are applying this to routed ports, then those routed ports must be connected to the same subnet. This would typically be done with an additional Layer 2 switch to which those routed ports connect.
In order for HSRP to function, the switch being used must function at Layer 3, and for this reason, the ip routing command must be enabled if you are using a multi-layer switch. However, in the lesson, this was not done. This could be because the specific model used by Rene has routing enabled by default, or because he simply considered it self-explanatory… In any case, the config in the lesson is indeed running multi-layer switches.
I hope this has been helpful!
Laz