# Fundamentals

What Kustom is, which of its products you're integrating and the four things that stay the same across all of them — the order, its lifecycle, the credential you send and the rules every API follows.

Kustom is a payments company, and Kustom Checkout is its flagship: a hosted checkout you embed
in your own store, so customers pay with local payment methods and live delivery options while
you keep the cart. Everything else in these docs — Order Management, In-store, Finance — is
what happens to that order before and after the moment of payment. This tab holds what stays
the same whichever of them you're integrating.

## Pick your path

Most stores connect without writing any code. Start with the path that fits you.

- **Your store runs on a platform** _(Most merchants)_ — Close to thirty platforms — WooCommerce, Magento, PrestaShop and OXID among them — ship a maintained Kustom plugin. Installing it *is* the integration. [Find your platform](/partners/)
- **You are building the integration** _(Live demo)_ — A working checkout in 15 minutes, with every call running for real beside the text on throwaway Playground credentials. The guide then takes it to production. [Start the quickstart](/checkout/quickstart/)
- **You are building with a coding agent** _(Agents)_ — Give the agent its own Playground API credentials and the Kustom skill, and it can create orders on its own. Every page has a Markdown version for it to read. [Set up a coding agent](/basics/for-agents/)

## What runs through every product

Whichever tab you end up in, four things are the same. Read them once. The last two live in
the API reference, next to the endpoints that assume them.

  The order

One object from cart to refund. Amounts in minor units, lines that must add up and the two snippets it carries.

[/basics/what-an-order-is/](/basics/what-an-order-is/)

  Authentication and environments

An API username and API password, sent as HTTP Basic, against a Playground host or the live one — never both.

[/api/authentication/](/api/authentication/)

  The order lifecycle

Incomplete → complete → authorized → captured, and who moves it at each step. Paid is not finished.

[/basics/order-lifecycle/](/basics/order-lifecycle/)

  API basics

Data formats, the error object, limits and idempotency — written once, true of every endpoint you'll call.

[/api/](/api/)

## What you own and what Kustom owns

The split is the same in every product, and most support tickets come from getting it wrong.

| You own | Kustom owns |
|---|---|
| **The cart math.** Line totals must add up to the order total. Kustom rejects a mismatch rather than correcting it. | **The checkout UI** and everything the customer types into it. |
| **Your callback endpoints.** Confirmation, push and optionally validation and shipping. | **Payment methods and the customer's payment data.** You never see a card number. |
| **Your own order record.** The push call is what tells you to create it. | **Authorization and settlement.** You capture. Kustom moves and pays out the money. |

## Related

- [Build a perfect integration](/basics/perfect-integration/) — how the products connect on one order, and the standard each stage is held to
- [How Kustom Checkout works](/basics/how-kustom-works/) — the four calls behind every direct integration
- [Express buttons](/checkout/surfaces/express-buttons/), [Sell to businesses (B2B)](/checkout/use-cases/b2b/) and [Charge a customer later](/checkout/recurring/) — features to add to the checkout
- [Test data](/basics/test-data/) — addresses and payment details that complete a Playground purchase
- [Find your platform](/partners/) — skip the code entirely if a plugin exists