After a transaction is made and broadcasted to the network, It goes to a temporary store known as the Mempool. In here, Validators verify pending transactions and add them to a new block usually based on the amount of gas spent for the transaction.

This is why during network congestions where there are high amounts of transactions, transactions with lower gas fee get added to the blockchain last thereby increasing the amount of time spent for the transaction to be complete.

After the block containing the transaction is added to the Ethereum network(ethereum chain), the transaction is said to be completed.