Confluence can backup all the content, comments and attachments for a space. The process involves converting the data in the space into XML format. The end product is a zip file that contains XML file(s) and optionally, all the attachments in the space. To transfer this data to another Confluence site, you simply restore this zip file.
Creating a Space Backup
Instructions on how to create a backup for a space can be found here.
Restoring/Importing a Space Backup
Instructions on how to restore or import the backup of a space can be found here.