A blockchain node is an application that allows users to participate in a blockchain network. Substrate-based blockchain nodes expose a number of capabilities:
* **Networking**: Substrate nodes use the [`libp2p`](https://libp2p.io/) networking stack to allow the nodes in the network to communicate with one another.
* **Consensus**: Blockchains must have a way to come to [consensus](https://docs.substrate.io/fundamentals/consensus/) on the state of the network. Substrate makes it possible to supply custom consensus engines and also ships with several consensus mechanisms that have been built on top of [Web3 Foundation research](https://research.web3.foundation/Polkadot/protocols/NPoS).
* **RPC Server**: A remote procedure call (RPC) server is used to interact with Substrate nodes.
There are several files in the `node` directory. Take special note of the following:
* [`chain_spec.rs`](https://github.com/paritytech/polkadot-sdk-solochain-template/blob/master/node/src/chain_spec.rs): A [chain specification](https://docs.substrate.io/build/chain-spec/) is a source code file that defines a Substrate chain's initial (genesis) state. Chain specifications are useful for development and testing, and critical when architecting the launch of a production chain. Take note of the `development_config` and `testnet_genesis` functions. These functions are used to define the genesis state for the local development chain configuration. These functions identify some [well-known accounts](https://docs.substrate.io/reference/command-line-tools/subkey/) and use them to configure the blockchain's initial state.
* [`service.rs`](https://github.com/paritytech/polkadot-sdk-solochain-template/blob/master/node/src/service.rs): This file defines the node implementation. Take note of the libraries that this file imports and the names of the functions it invokes. In particular, there are references to consensus-related topics, such as the [block finalization and forks](https://docs.substrate.io/fundamentals/consensus/#finalization-and-forks) and other [consensus mechanisms](https://docs.substrate.io/fundamentals/consensus/#default-consensus-models) such as Aura for block authoring and GRANDPA for finality.
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