To activate custom segments in AudienceReport, you need to edit the target group of your campaign. Mind that you can both activate the custom segments that are made available by default or activate your own custom segments if you have had any uploaded to your AudienceReport account.
If you want to activate a custom segment to a brand new campaign, you create a new campaign and then click on "Add a custom segment" in the bottom of the "Target Group" section.
You will then be able to choose the preferred custom segment by clicking on "Add".
If you want to activate a custom segment in an already existing campaign, you will need to click on "Actions" on the right side of the relevant campaign and then on " Edit Campaign". From here you will select the "Target group" tab and click on the " Custom Segment" at the bottom of the section (see above).
By simply adding the custom segment to the target group, the profile details will be reported on the custom dimensions. However, AudienceReport also allows you to define (narrow) your target group by any combination of responses from the custom segment questionnaire sent out to AudienceReport panelists. For example, you will be able to see the effects of your campaign exclusively for those users who claim they "definitely" want to buy a new car soon, or maybe those who "probably" want to do so.
As you can see, by narrowing your target group with target segments, you will see a different overview. In the first image you can see the campaign without any selected custom segments, hence showing "reach" as a dimension. In the second one, with implemented custom segments, you can see the "coverage" dimension instead
Mind that these choices will affect reach (now coverage), affinity and share in target group reported on the campaign.