There is a REPL at the site where you can write code and run it in the browser.

In a .svelte file you can have a script tag, markup (HTML) and a single style tag that contains all of the styles.

<h2>My first Svelte component</h2>

<p>Hello World</p>

<a href="https://www.youtube.com/lihautan">Link to Li Hau's youtube</a>
<a href="https://www.youtube.com/@henrikvilhelmberglund">Link to my youtube</a>

You can import a .svelte file from anywhere and use it like a class like this:

<script>
  import MyComponent from "/src/lib/MyComponent.svelte"
</script>

<MyComponent/>