The simplest way to get this to work is to start with a document that has footnotes, and then to use the “Detach” function in Footwork to detach the footnotes. When you allow Footwork to detach the footnotes, it sets everything else up so that it just works.
However, if you cannot do that because the footnotes are supplied as a separate text, then there are a few steps that have to be taken and these are described in the User Guide starting on p. 17.
The basic error message you’re getting is saying that Footwork expects you to tell it which text frame contains the footnotes, and which frame contains the main text. You should give the first frame of the main text some name in the Layers panel (make sure to name the text frame, and not the layer its in). Then you should give exactly the same name to the first text frame of the footnotes text, but add a * at the end. So if the first text frame of the main text is called “Chapter1” in the layers panel, the first frame of the footnote text should be called “Chapter1*”.
But since other steps are required as well, for testing purposes and until you get a hang of the software, I really recommend starting with some text that has regular InDesign footnotes, and then using Footwork to detach them.
The User Guide comes with a Quick Start section (on p. 4).
Hope that helps, if you have any other questions post back!