In order to participate in the Ethereum network, users download the software and run it on their computer. Computers running Ethereum software connect to form a peer-to-peer network. Each computer independently calculates and stores three data structures: The execution chain (Ethereum Virtual Machine, or EVM), the Beacon chain (for consensus), and the state (account balances, contract storage, etc.).
Once the software is installed and running, the computer becomes a full node and seeks out connections to other computers, or peers, who are also running Ethereum. As a full node, the computer then ‘asks around’ for the Ethereum blockchain, always accepting the chain with the most accumulated votes as the correct chain.
Once the blockchain is downloaded, the full node will re-verify both the transactions and the votes in the blockchain to ensure none of the protocol rules have been violated. The state is then updated to reflect the latest transaction outcomes.
The full node will request from its connections the ‘waiting list’ of known signed transactions that have not yet been added to the blockchain. It then re-verifies these transactions to ensure no rules have been broken, before adding them to its own waiting list. This waiting list is called the mempool. After assembling its own mempool, the full node will constantly receive transactions from its network peers, verify them, and relay them to its other peers, ensuring that valid signed transactions are propagated across the network.