You can find your Cerkl's segments under Audience > Segments. You can use the segments feature when you upload subscriber lists (you can upload to a certain segment!).
You can send content to specific segments in Content Manager by clicking the orange gear icon to bring up Distribution Settings > Segments. Then select the segments that you want to see the content, and choose whether or not you would like to restrict the content to those segments.
You can also send content to specific segments when creating a Blast. When creating a dedicated email, scroll down to the "Segments" box, and type in the segments you would like to send the email to.
Think of segments as the demographics of your subscribers (i.e. age, sex, location, profession, etc.). Segments are not your subscriber's interests. Our categories feature (Settings > Topics) organizes your organization's topics to inform the interests of your audience.
You can read more in-depth about segments here.