You may want to send your campaign to a specific group of attendees. For example a reminder email to attendees who have registered and belong to a specific group you have set. You can achieve this using operators: AND, and WITHOUT.
To get better understanding of how you can target groups of people using logical operators, let's take two teams: A & B. Some people belong to A, some belong to B, and some belong to both teams.
Team A AND Team B gives all the people belonging to A and all the people belonging to B.
Team A WITHOUT Team B gives the people belonging to A and removing the ones also belonging to B.
Let's try something more concrete. You want to send a reminder email to attendees who have not yet registered (Awaiting answer). However this reminder email is for attendees arriving by plane. You do not want the attendees arriving by train to get it.
First, make sure you have a group which includes all the attendees arriving by plan called 'Plane". Then think about it :
You want to target the population in the group "Plane" but only with the registration status 'Awaiting answer". You want to send an email to group "Plane" WITHOUT the ones "Confirmed" and WITHOUT the ones "Declined"