# Tutorials (/docs/tutorials)

Each tutorial builds one small thing that works from start to finish, in test mode.

<Cards>
  <Card title="Hello World" href="/docs/tutorials/hello-world">A browser checkout in one HTML page: get a limited token, create a cart, pay with a test card and show the result.</Card>
</Cards>

## Usage billing [#usage-billing]

Bill customers for what they use. Each tutorial runs in test mode and builds on the first one.

<Cards>
  <Card title="Bill for API calls" href="/docs/tutorials/bill-for-api-calls">Count calls in your server, send them in batches, and price them with calls included and tiers.</Card>
  <Card title="Bill for seats" href="/docs/tutorials/bill-for-seats">Send a seat count every hour and bill the most seats used in the month.</Card>
  <Card title="Sell prepaid credit" href="/docs/tutorials/sell-prepaid-credit">Charge a credit pack and add the credit when it is paid, so usage is paid from it first.</Card>
  <Card title="Show usage in your app" href="/docs/tutorials/show-usage-in-your-app">Show usage so far as a bar, and email customers at 80% of their plan.</Card>
</Cards>

New to the API? Run the [Quickstart](/docs/getting-started/quickstart) first. It makes the test product the Hello World page uses.