There are two segment specific exports Segment performance and Segments - Visitor breakdown.
DANGER: The segment exports mentioned above will not work with properties that are using non-default or non-transactional events as conversions. More information is available by reaching out to Customer Support
Select Segments from the side menu and open a segment from your list of segments
Select and then Generate export:
Enter a name for your export in the field provide and select which segment report you would like to generate:
Select Configure report
You can now configure the export to include additional segments, the date range you wish to report on, including any dates within the reporting period you wish to exclude, dimensions, and metrics. See Creating and configuring exports for more information.
When you have finished configuring the export, select Generate report