Why current switch packet mentioned of voltage and ampere?
It's not about how much power the switch consumes (none as you observe), it's about how much power the switch can pass through, and succesfully interrupt when you turn it off.  

Amps indicates the capacity of the internal circuit paths in the switch, and the ability of the switch to interrupt a load.  Note this rating will be different for resistive vs. inductive loads, different for DC, and even more different for a DC inductive load.  This switch is not rated for DC, at least, it's not stated on the front.  

Volts indicates the quality of the insulation within the switch, and its ability to resist voltage arcing across the contacts (aside from inductive arcing). 

This one is sized, tested and hopefully listed  to be used in mains power lighting circuits in places like the UK and India, where lighting circuits are typically fused for 6A. 

The labeling warns you not to switch too large a load (e.g. a heater) or switch too high a voltage (e.g. a 400V circuit, a common voltage available by taking two phases of the mains supply voltage). 



A sidebar on the USA.  UK 6A lighting circuits give 1440W of usable power, which is quite a lot less than UK's 13A receptacle circuits (3120W) or mainland's receptacle circuits (3680W).  This allows wire less than half the size.   

In the US, there's no special type of circuit for lighting, they're all 15A (1800W) or 20A (2400W) randomly (except for specialized loads, washer, oven etc.) The trend is to require 20A for more and more circuits.  You may notice the 15A circuit has barely more power than UK 6A circuits. That's why they don't bother having a smaller just-for-lighting circuit type. 14AWG (2.1mm2) is the smallest allowed wire size.  US rules allow the light switch to be sized appropriate to the load, but they still must be UL/CSA/TUV listed, and those listing agencies will require a switch to be able to interrupt 20A at least occasionally.