What is a blockchain?
A is a distributed, immutable ledger — a database replicated across thousands of computers worldwide. Each "block" contains a batch of verified transactions, chained cryptographically to the previous block. No single party controls it, and altering past records requires overpowering the entire network.
Blockchain = shared ledger no one can secretly change.
Proof of Work vs Proof of Stake
(used by Bitcoin) requires "" to solve complex math problems to validate transactions, consuming significant energy. (used by Ethereum after the Merge) selects validators based on the amount of they as collateral — far more energy efficient, but with different trade-offs.
Why decentralization matters
Traditional banking relies on trusted intermediaries. Blockchains replace trust in institutions with trust in math and code. This enables peer-to-peer transactions without banks, censorship-resistant applications, and ownership of digital without a central custodian.
Gas fees explained
Every action on a (sending , executing a ) requires computational resources. pay the validators who process these transactions. On Ethereum, fees spike during high demand, making the network expensive. Layer 2 networks (like Arbitrum, Optimism) process transactions off-chain and settle to Ethereum, slashing fees dramatically.
Gas fees are the cost of computation on a blockchain.