Segment name: the name of the segment
Active: if the segment is active, it means if it will show up in the campaign segment step
On top of this section you the total number of AcyMailing users selected with all the filters that you've selected. If you want to add a new filter simply click on the button Add filter, every time you mage a change the counter will reload. The count on the right of the filter is the number of users selected by the filter. You can delete a filter by clicking on Delete this filter.