BCH coins are created using a method called mining. Since BCH uses a decentralized network of nodes, there is no central entity in the system. Each block contains many transactions and is generated roughly every 10 minutes. The first node that manages to find the new block address is awarded with a set amount of BCH.
In order to mine Bitcoin Cash profitably, you will need ASIC miners, which require a large upfront investment. In addition, your machines would have to be located somewhere with competitive electricity costs.
For the vast majority of people, it makes more sense to simply buy some BCH rather than mine it.
If you are simply curious about the mining process, you could try to mine some BCH with your personal computer. However, don’t expect any profits – the amount of electricity you will be consuming will by far outweigh the value of any BCH you might earn.
Currently, there are 18.96M BCH coins available out of 21,000,000 total BCH. That means that the rest have yet to be mined and are currently unavailable for trading.