Hi,
Just have a Command Button on your UI. Under the EVENT_COMMIT for the command button you call the "FileSelectPopup" function which opens a browser to select the file. Then the file path is stored under the path which you can in turn use to open and write the data by the normal file operation commands.
In the example they are opening a file which already has the text and adding the other content based on the selection of controls on the UI. If you want to add any data, you can always open the file, write to it using the file operation commands with the data in strings and save it.
Regards,
Siddu