D1. Is a blockchain a database or a backend?

Web3 Architecture - Preethi Kasireddy

D2. Where can I learn Solidity?

Introduction to Smart Contracts - soliditylang.org
The official Solidity language docs with examples of basic smart contracts

CryptoZombies - cryptozombies.io
Interactive courses that teach you how to write smart contracts

The Ethernaut - OpenZeppelin
A game that teaches you how to interact with smart contracts using your browser’s console

D3. How do I put code on the blockchain?

Deploying Smart Contracts - ethereum.org

D4. How do I test my smart contract?

Testing Smart Contracts - ethereum.org

D5. How do I update a deployed smart contract?

Upgrading Smart Contracts - ethereum.org

D6. What are some useful development tools?

Hardhat - hardhat.org
Development environment for Ethereum software

Foundry - Foundry Organization
Smart contract development toolchain

Remix - Ethereum Foundation
Browser IDE for Solidity

D7. Where can I learn more about blockchain security?

Smart Contract Best Practices - ConsenSys Diligence
An index of known smart contract attacks and how to defend against them

Secureum Substack - Secureum
A newsletter on the topic of security related to Ethereum

Damn Vulnerable DeFi - The Red Guild
A series of coding challenges for learning offensive security of DeFi smart contracts

D8. What are bridges? Or other blockchains?

Blockchain bridges - ethereum.org

Optimism Standard Bridge walkthrough - ethereum.org

D9. MEV (Miner Extractable Value)

Flashbots 101 - Flashbots

D10. ZK (Zero Knowledge)

learn.0xparc - 0xPARC