You can tag a user by adding the ot_ prefix to an attribute. The following example illustrates how this is done, just add the following url attribute to the page where you collect the data, for instance an email:
Pageviews & duration
Sending events to Opentracker's events engine with a ot_ prefix in an attribute in the url, automatically updates the state of the session and the users. The state is updated in the user interface for the user, sessions and events. A cookie will hold the state informations.