We recommend that you use Time Machine to backup your data. If you backup your home folder, your Mental Case data will automatically be included.
You data is kept in this folder
Your home folder : Library : Containers : com.mentalfaculty.mentalcase.mac
The Library folder is hidden, so choose Go > Go to Folder in Finder, and enter this
~/Library/Containers
This will show the Containers folder, and you can navigate to the com.mentalfaculty.mentalcase.mac folder.
If you want to manually backup the Mental Case data, just select the com.mentalfaculty.mentalcase.mac folder in Finder, and choose Edit > Copy, then navigate to where you want to make the backup, and choose Edit > Paste.