A blockchain is a shared ledger that thousands of computers keep identical. Every few minutes a new block adds a batch of transactions, and each transaction says which coins moved, to where, and for what fee. Nothing else is written down: there are no names and no reasons.
Bitcoin counts coins as outputs
Bitcoin doesn't keep balances. It keeps a list of unspent transaction outputs, or UTXOs: individual chunks of bitcoin that are spent whole. Pay someone 0.2 BTC from a 1 BTC output and the transaction creates two new outputs, 0.2 for them and about 0.8 back to you as change. Your balance is the sum of the outputs your keys can spend.
That detail is what makes most of the indicators in this course possible. Because every output records when it was created, and a price existed at that moment, the chain tells us what each coin last cost and how long it has sat still.
Ethereum counts balances
Ethereum keeps one running balance per account, more like a bank ledger. Age and cost don't attach to individual coins in the same way, so indicators that depend on a coin's last-move price are defined differently there, and many are simply Bitcoin-only.
What the record can't tell you
The chain shows movement, not intent. A coin sent to an exchange might be sold, posted as collateral or just shifted between that exchange's own wallets. Good on-chain work starts from what was recorded and is honest about the step from there to why it happened.