What are you trying to get people to DO on your site? What is your conversion event? Of course, there are many different answers to this question, depending on your site type/vertical and your organizational goals. In any case, it is common in AAM to create traits for visitors who have met those criteria.
In AAM, there is a field where you can mark your trait as a conversion trait, especially for use in Audience Lab.
Also, when using events to create traits, there is a major gotcha that you need to keep in mind, so that you don't collect more users than you should into the trait. Watch this video for the big reveal. :)