A mobile Point of Sale (POS) system is actually a mobile device that gives users an opportunity to process sales transaction info at any place. In the past, people have used mobile computers for this purpose, but today you can use smartphones, tablets, phablets or other forms of mobile devices that have the power to process such transactions. Of course, in order to do this, the mobile device you are using must have suitable software. What kind of infrastructure or type of device and software you need depends on a few factors.
You may also want to read about the topic in India: https://help.shopify.com/en/manual/sell-in-person/payment-methods