Mining is a process where the cryptocurrencies are created. The computer will have to solve complex mathematical equations before a coin is created. You could make lots of money Mining cryptocurrencies.
With the mining of the pi coin it is a step away from it becoming a coin which can be used to trade. As of now those mining pi are just hoping it will become a coin of value later.
Its electricity consumption is higher than that of all other machines, it doesn't share an electric transformer with other appliances, and it uses a lot of power. These are serious issues, which is why the government always speaks out against it.
Cryptocurrencies that have Proof of Work Consensus mechanism can be created through complex mathematical problem solving, usually referred to as mining. In order to mine, you need hardware as well as software. I can't say much about Pi mining.