How can I use LO to create online help?

Are there any tools to create online help from LO source documents? Robohelp was once used to create online help from Microsoft Word documents.

Which type of the help file(s) do you want to create?

The LO can save the Writer documents into HTML format, and you can use Hyperlinks in the document.

It depends on which format of online help you are looking for.
As stated by Zizi64 Writer can save in HTML and you can also easily create TOC and index.

Have a look at