if you are a user of the system and would like to contribute text for the help screens, login to the ofbiz document system and create the pages in the 'wiki' and notify of this event in the mailing list or create a 'Jira' issue

If you are a contributor you can create the help screens by added some stuff in OFBiz documentation files.

The better way for how  to do that is to read documentation on chapter The Apache OFBiz documentation system.