> ## Documentation Index
> Fetch the complete documentation index at: https://docs.terratwin.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Guides

> Learn how to authenticate requests, manage usage, model shipments, and configure transport operations.

## Access and usage

Set up access to the API and understand how your usage is calculated.

<Columns cols={2}>
  <Card title="Setting up API keys" icon="lock" href="./authentication">
    Generate API keys, secure them, and use them to authenticate requests from your services.
  </Card>

  <Card title="How credits work" icon="coins" href="./credits">
    Learn how credits are consumed, how usage is calculated, and how to avoid unexpected consumption in production.
  </Card>
</Columns>

## Shipment structure

Learn how the components of a shipment fit together before configuring individual transport legs.

<Columns cols={2}>
  <Card title="Cargo" icon="boxes-stacked" href="./cargo">
    Define the cargo being transported and provide the information needed for emissions calculations.
  </Card>

  <Card title="Locations" icon="location-dot" href="./locations">
    Describe shipment origins, destinations, and intermediate locations.
  </Card>

  <Card title="Transport chains" icon="route" href="./transport-chains">
    Combine shipment legs into a complete transport chain from origin to destination.
  </Card>

  <Card title="Hubs" icon="warehouse" href="./hubs">
    Represent terminals, warehouses, ports, and other hubs within a transport chain.
  </Card>
</Columns>

## Transport operations

Configure shipment legs for a specific transport mode or use a fallback when complete mode information is unavailable.

<Columns cols={2}>
  <Card title="Road transport" icon="truck" href="./road-transport">
    Configure shipment legs transported by road.
  </Card>

  <Card title="Rail transport" icon="train" href="./rail-transport">
    Configure shipment legs transported by rail.
  </Card>

  <Card title="Water transport" icon="ship" href="./water-transport">
    Configure shipment legs transported by sea or inland waterways.
  </Card>

  <Card title="Air transport" icon="plane" href="./air-transport">
    Configure shipment legs transported by air.
  </Card>

  <Card title="Unknown transport" icon="circle-question" href="./unknown-transport">
    Model a shipment leg when the transport mode is unknown.
  </Card>

  <Card title="Weighted modes transport" icon="scale-balanced" href="./weighted-modes-transport">
    Model a shipment leg using a weighted combination of multiple transport modes.
  </Card>
</Columns>