What is Smart Contract
Definition: An agreement, contract, or set of instructions that is deployed on a decentralized blockchain. To achieve Trust Minimized Agreement
- can not be altered
- automatically executes
- everyone can see it
Transaction
Structure
Transaction Fee: whenever a transaction happens, transaction fee would be given to the node who are running the block chain software(miners).
Transaction Hash: The unique identifier of a transaction among a block chain network.
Gas: A gas fee is a blockchain transaction fee, paid to network validators for their services to the blockchain. The busier the network is, the higher the gas fee is.
In each transaction, part of the fee go to miners and part of burned
Why Block Chain is Immutable
All the block are linked and referred by the previous one with hashes. Any modifications would lead to invalid hash on a block which cause the following blocks invalid:
Keys
Digital Signature
In digital signature, public key encrypt and private key decrypt.
**Produce a signature: ** 
Verify a signature:
Private key -> Public Key -> Address
What is mint ?
Mint is a process that packages the new trading history and add it into a new block in the block chain. It requires computations to generate valid hash of the block chain for that block.
