This event element is used to react to user behaviour - once the recipient has clicked a link in the email, a tag can then be set or a new campaign started, for example.
To do this, connect the element to the sequence and open it with a double-click. On the left-hand side, you will see all the emails which contain trackable links. Click on the email and then on the link to which you want to react. If you want to react to all links in all the emails, you must also check the links in all the emails.