***

title: Core Concepts
sidebarTitle: Overview
description: The fundamental building blocks of the Atoms SDK.
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The Atoms SDK is built around a **graph-based architecture** where information flows between processing units. This design makes it easy to build everything from simple chatbots to complex multi-agent systems.

## How It Works

Every voice conversation in Atoms follows this pattern:

1. **Audio comes in** — The user speaks into their phone or browser
2. **Events flow through nodes** — Speech is transcribed, processed, and responses generated
3. **Audio goes out** — The agent's response is synthesized and played back

The system manages all the complexity of real-time streaming, interruptions, and state management. You just focus on the logic.

## The Four Building Blocks

<CardGroup cols={2}>
  <Card title="Nodes" icon="circle-nodes" href="/atoms/developer-guide/introduction/sdk/nodes">
    Processing units that handle events. The brain of your agent logic.
  </Card>

  <Card title="Events" icon="bolt" href="/atoms/developer-guide/introduction/sdk/events">
    Messages flowing through the system. Audio, text, and control signals.
  </Card>

  <Card title="Graphs" icon="diagram-project" href="/atoms/developer-guide/introduction/sdk/graphs">
    Connect nodes into pipelines. Build complex multi-agent flows.
  </Card>

  <Card title="Sessions" icon="clock" href="/atoms/developer-guide/introduction/sdk/sessions">
    Manage conversation state and lifecycle. One session per call.
  </Card>
</CardGroup>