You can track visitors who have converted on your website or have clicked on a Marketing email link (assuming that they haven't blocked cookies on their browser).
You will be able to track people under the following circumstances:
- they have submitted a form on your website
- they have submitted a Lead Flow on your website
- they have submitted a Meetings link that was hosted with your domain
- they have clicked on a link sent from the Marketing Email tool
Assuming that they are not blocking cookies, then you can track under any of the circumstances above.
You cannot track people on your website if they are clicking on a link in a one-to-one email sent using the CRM. This is because they haven't necessarily consented to your tracking. This ensures that you remain compliant with the GDPR.
You can read more about HubSpot tracking here: https://knowledge.hubspot.com/articles/kcs_article/account/how-does-hubspot-track-visitors