To export a collection, navigate to the Collections page and click on the collection. Click the Export Collection button in the top right.
This will start the collection export and navigate you to the Job Detail page, where you can view the progress.
Cloudpress will only export pages in the database that have been changed since you previously exported them. For example, in the job log below, you will notice that Cloudpress skipped all the pages since they have not changed since the previous export.