To Import a GML Data Source

Right-click on the Import node and select Add GML File.
A dialog displays prompting for the data file and , optionally, a schema file. Use the browse buttons to locate the data file. If the Specify Schema option is not toggled then import process will attempt to find the schema file. Alternatively you can select the Specify Schema and manually select the schema file corresponding to the specified data file.

Note: The schema file is optional. Use the check box (unchecked by default) to enable the schema text box. The same applies at export.

Effect at import: the import process will try to find the schema file by itself. It needs to be at a valid relative location from the GML file, or can be an absolute path, or it can be on the web.

Effect at export: if present, the export process will use this file; if omitted, an XSD file will be created based on the current XFM schema. Note that subfeatures are not supported.
The available features are displayed in the interface. See the description in To import a GIS file to set symbology, area etc.