Based on information gathered from your members' activity (e.g. date they were added to your list, number of times they have opened a campaign, number of times they have clicked on a link, etc.) you are able to create your segments and filter them as you see fit.
You can even set multiple segmentation criteria, and narrow down the list of recipients contained inside your segment. This way you will send fully targeted campaigns to the people most likely to respond positively to one of them.
During the list segmentation procedure you will have to take the following steps:
1. Once inside your mailing list, click on the Segments button.
2. Tap on Create segment.
3. After naming your segment, specify whether your segment needs to fulfill All or Any of the criteria you set by using the second drop-down menu, as well as the contacts on which these criteria will be applied by clicking on the Preview recipients option on the right.
4. Tap on Add Criteria to further adjust the conditions of your segment.
5. When you are done, click on the Save segment button.
If you feel you need to learn more about segmentation before creating your own list segments, it's worth looking at a concrete example on how you can create a segment out of recipients who haven't opened a specific email campaign that you have sent out.