Call them storylines, main plot and subplots, or central plot and B-Plot, C-Plot. Whatever you call them, the chances are that your story actually consists of several threads. In the STORYLINES modus, assign each event in your story to one or more storylines, and then check the dispersal within your entire narrative with the Highlight function. Or choose the filter function to see only the event cards of one storyline and hide all the others, in order to concentrate on structuring this particular thread.
Read background information on Storylines here.