Next to "Select Database to Export" is a drop down menu listing the sections of the database that can be exported.
If you select one of the sections and then click on "Export", a file named (tablename).en_US.(timestamp) is written to the /usr/share/freemed/data/en_US directory. Before you do this, you have to set the permissions to 777 in the /usr/share/freemed/data/ and /usr/share/freemed/data/en_US/ directories.