i'm really confused what is thr purposes of the alternative coins and how this will be invented? and what are the good benefits of this alternatuve coins?

to me i think the main reason for creating an alt coin is to provide several online services to the people, but some people are creating it for generating money and nothing else.
It's definitely for online purpose, it was created to give us a very fast and cheap transaction. With bitcoin, we can also transact anonymous and it is the complete opposite of the bank, where it has been operated in a decentralized way while banks are centralized.
Thats actually the main purpose why bitcoin has been created and we could able to read that on the whitepaper of bitcoin which it focuses on online money transfer transaction without any 3rd party involve like government. Which it means its total decentralized and no one would able to control it. Bitcoin could able to stand on its own without any altcoin exist.