Comment on page
This part of the page is a summary of the previous step: recipients, you can see which lists you've selected and the total number of users subscribe to these lists.
This part of the page is where you can add a segment to your campaign. There is 2 way of doing it:
If you create a segment for this campaign and you would like to use it again after you can save it by clicking on the button Save segment on the right of the section.