So, how do Meta Mask coordinate all that?

As mentioned previously, an essential function of a blockchain network is coordinating the process of agreement between all the nodes in the network regarding whether a transaction is valid or not. The agreement is referred to as consensus, and the process by which it occurs is called a consensus mechanism, or consensus protocol. Ethereum has used two different consensus mechanisms at different points, the first being Proof of Work (PoW) and the second, Proof of Stake (PoS). In both mechanisms, computers are provided to do the work of verifying the validity of the transactions, and agreeing on them.