Once you’ve saved the download file, you can use Site Admin > Tools > Import > WordPress from another WordPress site to import this data.
Note: this export process does not save any site images. You will need to manually export any site images you want to keep. For more information about export media, visit https://wordpress.com/support/export/#exporting-the-media-library
For more general site export information, visit en.support.wordpress.com/export/