If you want to create metadata yourself (User defined), you must do it in the following manner:

After opening the Metadata Editor, you must add a desired number of fields by clicking the plus sign, set up their names, their data types, their delimiters, their sizes, formats and all that has been described above.

For more detailed information see Metadata Editor.

Once you have done all of that, you must click either OK for internal metadata, or Next for external (shared) metadata. In the last case, you only need to select the location (meta, by default) and a name for metadata file. When you click OK, your metadata file will be saved and the extension .fmt will be added to the file automatically.