At this point, you've created a new configuration file! You can check it for syntax by selecting the Validate XML File item from the Debug menu. The Open dialog is displayed; select your file and click the button. If all is well, a dialog box will display that says "OK". If not, you'll get a completely incomprehensible error message. About the only useful part of that message is the line number. Re-open the editor to that line and try to see what's wrong with the syntax.
Once you have a decoder definition file that checks out for syntax, you need to try it in DecoderPro. Your new file should copied into the jmri decoders folder (windows C:\Program Files\JMRI\xml\decoders).
When you are happy with your definition, you'll probably want to share it with the JMRI world, so next we'll look at submitting the definition to JMRI for inclusion in the next release.