A BITCOIN TRANSACTION UNDER THE HOOD:

(Definitions of the terms that are *in bold* follow)

When Ali sends those sats to Benji, the payment transaction is broadcast to the network.
The transaction gets validated by nodes that make sure Ali really has the bitcoin to send, and that it has not previously been spent (to prevent double-spending).
Once validated by a node, it waits in the mempool with other peoples' transactions.
The transactions in the mempool get added in a block to the blockchain when a miner finds a nonce that satisfies the difficulty algorithm.
Each block has a timestamp.
This creates immutability , and helps protect the difficulty algorithm adjustment from being manipulated.
Each block represents one confirmation for the transactions included in it.
As blocks are added, on average every ten mins, the immutability of the blockchain increases.