Using the code component, you can create custom components using HTML and Javascript. External javascript libraries can be included using their CDN links.
Example: Adding the Solana API to your site.
// include the library like this
<script src="<https://unpkg.com/@solana/web3.js@latest/lib/index.iife.js>"></script>
// access the library functions in your code
console.log(solanaWeb3);
var keypair = solanaWeb3.Keypair.generate();
Some example uses are: