Basically, cryptocurrencies are entries about token in decentralized consensus-databases. They are called CRYPTOcurrencies because the consensus-keeping process is secured by strong cryptography. Cryptocurrencies are built on cryptography. They are not secured by people or by trust, but by math. It is more probable that an asteroid falls on your house than that a bitcoin address is compromised. When it comes to other, less popular cryptocurrencies, the buying options aren’t as diverse. However, there are still numerous exchanges where you can acquire various crypto-coins for flat currencies or Bitcoins. Face-to-face trading is also a popular way of acquiring coins. Buying options depend on particular cryptocurrencies, their popularity as well as your location. To realize digital cash you need a payment network with accounts, balances, and transaction. That‘s easy to understand. One major problem every payment network has to solve is to prevent the so-called double spending: to prevent that one entity spends the same amount twice. Usually, this is done by a central server who keeps record about the balances. If this sounds similar to banks’ high-yield savings accounts or money market accounts, it is. The largest difference lies in the ability for yields on money market mutual funds to rise proportionately with interest rates. For example, as interest rates have risen, the yields on most bank money market accounts (which are set by the banks themselves) have stayed relatively flat, while money market mutual fund yields have increased.
Over time, money market fund "depositors" felt more and more secure, and not really at risk. Likewise, on the other end, corporations saw the attractive interest rates and incredibly easy ability to constantly roll over short term commercial paper. Using rollovers they then funded longer and longer term obligations via the money markets. This expands credit. It’s also over time clearly long-term borrowing on one end, funded by an on-demand depositor on the other, with some substantial obfuscation as to what is ultimately going on in between.