Signing data with ECDSA I was reading about the math behind bitcoins in this article, and one thing I can't seem to wrap my head around is how the said algorithm is used to sign "data". What exactly is this "data"? Is it my bitcoin? If so, how exactly is a bitcoin represented in terms of data? Say I have 5 bitcoins in my Coinbase wallet that I want to send my friend. How would that translate to the whole "gaining the private key and signing your data with it" process as described in the article?

Sorry if this is too novice a question, I'm new to cryptography concepts. Thanks in advance!
Every Bitcoin in existence today exists as an unspent transaction output (UTXO) on the Bitcoin blockchain. That is, the output of an existing confirmed transaction that has not yet been consumed as the input of some other transaction.

Coinbase has a collection of UTXOs that represent the Bitcoins that they hold. When you tell Coinbase to make a Bitcoin payment to someone from your wallet, they choose one or more of those UTXOs to make the payment with.

They then form a chunk of data that claims those UTXOs and creates a new UTXO giving the Bitcoins to the recipient and one giving any change back to them. It's that chunk of data that they sign with the key for each UTXO they are spending with that payment.

Once the transaction is confirmed, the new UTXO for the recipient is the Bitcoins you sent them. When they see that UTXO appear on the blockchain, they know you paid them. They can then form a transaction that spends that UTXO to transfer those Bitcoins to someone else.