I would assume from your question that you are asking how to create a GEDCOM?
As it's a data format for transferring information between different Genealogical oriented computer applications.
So you pick your favorite tool for creating family informations, and in that tool, once you have your family tree entered into it: you export a GED file.
Updates to the information that would be used to create a GED file are made in that application. When you like the current state of the tree, you can export it for transfer to another place (like to Wikitree).
If you can post a bit more info, I am sure many folks online here can help further.