Each square is a bitcoin address (like a public key)

Each graph component is a transaction. The components appear as transactions are broadcast into the bitcoin P2P network (but before they are verified and committed to the blockchain)

Coin ownership flows from green to red (yellow is in/out: I pay you and take some change back)

When the output of one transaction becomes an input for a new transaction, the components are pulled together

This gives you a sense of how money is changing hands in the global bitcoin economy