You buy them on an exchange. I use Coinbase. You ACH money from a checking account, buy the currency you want. You can transfer the crypto to a private “wallet” that is not connected to the internet. No can access that without your “keys”.
When you want to cash you, you simply reverse the process.
That is a very simple explanation. Thanks.
Question- if the "wallet" is not connected to the internet, how do you acess?