Notes and ledgers are the 2 ways to represent and circulate value.
Notes are an anonymous, nice way to keep and exchange value. But they can be lost, stolen, destroyed or created from zero. Instead, ledgers are a much intelligent way to keep track. They make value 100% traceable, transactions validity, etc.
In the digital world you can´t have digital value itself. The only way to keep track of value are the ledgers. The ledgers are a database that keep all the transactions with the date, amount, which account come from, and which account it went to.
And if you keep a unique, secure and consistent list of all those transactions then you got a digital system of value storage and transfer. You´ll still use money as value representation, but it can be applied to any concept of value.