You may find that as you are creating, searching through, and using segments, that you need to add a person's profile to the system.
You can do this directly from a segment:
1. With the segment open, click on the blue plus sign. The Add New User form will open.
2. Complete the form, making sure to fill in each required field so you can move on to the next section.
3. When all details are entered, click Add. The person's profile will now be in the segment, and in the system.