A track event is a named event that you've defined. Adding a track event is useful if you want to be able to be alerted (see alerts) or search for sessions where the user has done an action.

You'd like to see what users are doing that cause them to open the shopping cart. In your app, you'll add H.track():

import { H } from 'highlight.run';
import { getSubtotal } from '@utils';

const ShoppingCard = ({ items }) => (
    <Button
        onClick={() => {
            H.track("Shopping Cart Opened", {
                subtotal: getSubtotal(items),
                numberOfItems: items.length
            });
        }}
    >
        Shopping Cart
    </Button>
)

See the Recording Network Requests and Responses API documentation for more information on how to use it.