Lesson 4: Transactions, Fees, and the Mempool

Goal: understand what happens after you press “send” and why fees sometimes get wild.

Beginner

When you send bitcoin, you’re asking the network to add your payment to the big shared record. Sometimes lots of people are sending at once, so you might need to pay a higher fee to go faster.

Intermediate

Your transaction first goes to the mempool (a waiting room). Miners choose transactions to include in the next block. Because block space is limited, miners usually pick transactions with higher fees.

• Fees are not based on the amount of BTC you send, but on transaction “weight/size.”
• Busy network = crowded mempool = higher fee rates.
• Confirmations happen once a miner includes your transaction in a block.

Expert lens

Nodes maintain mempools locally; there’s no single global mempool. Transaction selection is miner policy, and fee rates are bid via sat/vbyte. Congestion reveals the base layer’s role as scarce settlement space.