Blockchain Basics Module
Blocks & Transactions
How a single user action becomes ordered blockchain history over time
Core path (one-hour): User intent → Transaction creation → Mempool → Block inclusion → Confirmations → Recorded history
This is the required path to complete the module. All other articles are optional.
Start core pathWhat this module covers
By the end of this module, you will be able to explain how a wallet action becomes recorded blockchain history — and why that history is not immediately final.
This module is for
- Wallet users who want a system-level mental model
- Developers who need the transaction→block→history pipeline
- Anyone trying to understand pending, confirmed, and reorganized transactions
This module is not
- Investment advice or asset selection (“what to buy”)
- Price predictions, trading strategies, or alpha
- Deep consensus proofs or protocol design
Stage 0
Orientation
What kind of system am I about to learn — and what problem does it solve?
Build the correct mental model for the rest of the module.
Keyword hooks: transaction lifecycle, mempool and propagation, block ordering, confirmations and reorgs.
High-level flow (details come later):
- Transactions encode user intent.
- Mempools collect competing transaction proposals.
- Blocks impose a provisional order on transactions.
- Linked blocks preserve historical consistency.
Core
Required to continue the module.
What Is a Blockchain?
Supporting (intuition)
Optional intuition and mental models. Optional. Helps fix common mental model mistakes early.
What You Actually Own on a Blockchain
What Is a Cryptocurrency? (Beginner Guide)
You can move on when:
- You can name the objects: users, transactions, mempool, blocks, chain history.
- You can point to where each object fits in the flow (without details yet).
- You can explain why “seeing a transaction” does not mean it’s final.
Stage 1
Intent & Proposals
How does a user express an action in a blockchain?
Understand what a transaction represents and what it commits to.
Core
What Is a Transaction?
Transaction Lifecycle: From Wallet to Network
Supporting (intuition)
Optional intuition and mental models.
What Are Cryptographic Keys (Private vs Public)?
What Is a Crypto Wallet? (Hot vs Cold Wallets)
What Is a Seed Phrase and Why It Matters?
Why Transactions Need Signatures
Crypto Addresses: What They Are and How They Work
Why Transactions Must Be Ordered per Sender
Accounts vs UTXO: Two Models of Spending
Why Transactions Can Fail or Be Rejected
Reference (how to observe the system)
Optional verification via explorers, clients, wallets, and documentation.
Transaction Statuses Explained (sent / pending / failed)
What Transaction Receipts Really Mean
You can move on when:
- You can explain a transaction as a signed proposal (not acceptance).
- You can explain why signatures and nonces exist at a high level.
Stage 2
Competition & Visibility
Why is “pending” local and inclusion uncertain?
Understand why visibility ≠ inclusion and what influences whether a transaction gets included.
Common confusion
“I see it in my wallet/explorer, so it’s accepted.” Not necessarily: mempools are local and inclusion is competitive.
Core
Mempool & Propagation
Supporting (intuition)
Optional intuition and mental models.
Why Fees Exist on Blockchains
Gas and Fees: The Basic Mental Model
Fee Markets and Congestion (High-Level)
Why Fees Change Over Time
Transaction Replacement (Speed Up / Cancel)
Why Different Nodes See Different Mempools
Why Transactions Get Dropped or Delayed
Reference (how to observe the system)
Optional verification via explorers, clients, wallets, and documentation.
Common Wallet Messages (pending / dropped / replaced)
You can move on when:
- You can explain why two honest nodes can disagree about what’s pending.
- You can explain (in one sentence) why a transaction might be dropped or replaced.
Stage 3
Ordering & History Formation
How does the system impose order on many proposals?
Understand what a block decides and how it turns proposals into recorded history.
Core
What Is a Block?
Supporting (intuition)
Optional intuition and mental models.
Why Blocks Are Linked Together
Block Size and Capacity Constraints
Genesis Block Explained
Hashing in Blockchain
Why New Blocks Are Not Seen Instantly Everywhere
Reference (how to observe the system)
Optional verification via explorers, clients, wallets, and documentation.
What Is a Blockchain Explorer?
Time, Blocks, and Average Block Time
You can move on when:
- You can explain what a block decides about ordering and inclusion.
- You can explain where to look to verify inclusion (without needing consensus details).
Stage 4
Stability Over Time
Why does history become more reliable over time?
Understand what confirmations measure and why short reorgs happen.
Core
Confirmations & Reorgs
Supporting (intuition)
Optional intuition and mental models.
Why Recent Blocks Can Change
What Is a Fork in Blockchain? (Soft vs Hard)
Reference (how to observe the system)
Optional verification via explorers, clients, wallets, and documentation.
Why “Confirmed” ≠ “Final”
You can move on when:
- You can explain what confirmations measure (and what they don’t).
- You can explain what a reorg is and how it can change “confirmed” history.
Stage 5
Boundaries & Next Module
What is NOT explained here, and where does it lead?
Close the loop and clearly point to consensus and finality without adding new mechanics.
This stage adds no new mechanics. Consensus and finality are covered in the next module.
Out of scope (intentionally)
- How blocks get chosen: miners/validators, fork choice, and “who decides”
- Why one chain becomes shared history (consensus)
- What “final” means and how finality is achieved
Questions for the next module (Consensus & Finality)
- How do nodes agree on one chain when they see different blocks?
- What is consensus, and what is it optimizing for?
- What is finality, and how does it differ from confirmations?
Supporting (intuition)
Optional intuition and mental models.
What Is Consensus?
From Confirmations to Finality
Why Finality Differs Across Blockchains
You can move on when:
- You can state what’s out of scope for this module.
- You can name the next questions and the next module that answers them.
Module completion
If you can answer these, you finished the module.
- What is a blockchain system trying to provide (in one sentence)?
- What does a transaction represent, and why isn’t it acceptance?
- Why can two honest nodes disagree about what’s pending (mempool)?
- What does a block decide about transactions, and what does it not guarantee?
- What do confirmations tell you, and what risk still remains?
- What is out of scope for this module, and which module comes next?
FAQ
Key concepts
Back to Blockchain Basics
Blockchain Basics hub
Next module
Consensus & Finality
How networks resolve competing blocks, choose canonical chains, and provide safety guarantees against reorgs.