> ## Documentation Index
> Fetch the complete documentation index at: https://yuno-3979e326-2026-05-13-universal-sdk-proposal.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Basic Concepts

To understand how Yuno operates, you need to grasp some fundamental concepts about its architecture. This guide covers the essential elements required for integration:

* **Sessions**: The most basic component of a transaction. A session begins when a user visits your checkout page and views the available payment methods. It contains all relevant checkout information, including available payment methods and tokenized options for returning users.

* **Payments**: A payment occurs when a user initiates a payment action during a checkout session.

* **Transactions**: These represent operations related to payments, such as purchases or refunds, processed through one or more connections.

<Frame>
  <img src="https://mintcdn.com/yuno-3979e326-2026-05-13-universal-sdk-proposal/hyxqUBLTyaWgYpeU/images/reference/basic-concepts/image1.png?fit=max&auto=format&n=hyxqUBLTyaWgYpeU&q=85&s=e43b1ef5ee39cd4b73d02870b58b4e67" alt="Transactions and Sessions" width="4074" height="3018" data-path="images/reference/basic-concepts/image1.png" />
</Frame>

## Concept list

For a deeper understanding of each concept related to Yuno's system, visit the respective pages:

<Columns cols={2}>
  <Card title="Customers" href="/docs/customers" arrow />

  <Card title="Sessions" href="/docs/sessions" arrow />

  <Card title="Payments" href="/docs/payments-1" arrow />

  <Card title="Transactions" href="/docs/transactions" arrow />

  <Card title="Tokens" href="/docs/tokens" arrow />

  <Card title="Payment Methods" href="/docs/payment-methods" arrow />

  <Card title="Fraud Prevention" href="/docs/fraud" arrow />

  <Card title="3DS" href="/docs/3ds-1" arrow />
</Columns>