you need a a gpu rig which is a computer that run with 6 gpu and mine the altcoin, you sell these altcoin for bitcoin on exchange and get your profit, thise gpu miners are expensive, if you don't have $1500 ready to invest forget about it, yes you can always mine with one gpu but don't expect huge profit
That ain't true at all. You must buy a good GPU, just one if you can't afford more, check out this forum often and you'll learn a lot. I'll explain mining to you with an analogy.
Let's say Bitcoin is the US dollar. They all go through banks and the government (so pretty centralized) and so through the hands of clerks, accountants, etc. These people handle your transactions, they make the money move and all that. In the Bitcoin "banking system" there are no actual banks and government but the clerks exist, they are the miners. They take care of the transactions and make sure the network is staying stable. They establish the consensus of who has what money but here everything is decentralized, there is no government that can shut it down.