If you are required to either Import or Export a Unit, you can do this within 'System > Import and Export'.
If you are required to take an export of a Unit - in the Export section, click the 'Export a unit' button. You will now be presented with a list of units; select the Unit you want to export and click OK. Finally, choose a filename and location for the file that will be created and click Save; TM will now export the selected unit to a v2z file in your chosen location. Once complete it will display 'The database has been exported' and show the path where it has been exported to.
Note: The v2z file that is created is essentially a zip folder containing XML files. You can rename a v2z file into a zip folder to explore the contents or extract specific XMLs. These exports do not include every table from the database, so some system settings such as TM Exchange settings will not be backed up this way.
Alternatively, if you have a v2z that you need to import, click the button 'Import single unit' in the Import section. Navigate to the v2z file that you have saved and Open. It will now import the selected file and will display a popup window notifying you when the Import is complete.