Hi, @lfcipriani from Twitter Platform Relations team. Twitter Cards Analytics is open for every account that has Twitter Cards installed (https://dev.twitter.com/docs/cards). It's a way to know how your content is shared on Twitter.
Then, every tweet (from any person in the network) that includes a link from your website will expand a Card and engagements data will be collected in your dashboard.
To install a Card you need to insert meta tags in your HTML page and get it validated in https://dev.twitter.com/docs/cards/validation/validator. The approval is automatic.
Then, every tweet (from any person in the network) that includes a link from your website will expand a Card and engagements data will be collected in your dashboard.
More info: https://dev.twitter.com/docs/cards/analytics