Lesson 5: Blocks, Mining, and Confirmations

Goal: understand why blocks exist, what miners do, and how confirmations reduce reversal risk.

Beginner

Bitcoin transactions are grouped into “blocks.” Miners work to add the next block. When your transaction gets into a block, it starts getting confirmations.

Intermediate

Mining is a competition to find a valid block by doing lots of hashing (proof-of-work). The winner broadcasts the block; nodes verify it; then the chain advances. Each block stacked on top makes earlier blocks harder to change.

• 1 confirmation = included in a block.
• More confirmations = more work would be required to reorganize history.
• Miners are paid via block subsidy + transaction fees.

Expert lens

Proof-of-work ties chain security to real-world costs. The “most-work chain” rule resolves forks. Finality is probabilistic: reorg probability decreases as depth increases, assuming honest hashrate majority.