Brainstorming is a feature where, after identifying a context source, if you’d like some inspiration as to new story angles that you might apply to that context, you are presented with selectable options in the form of topics and keywords. Click the green lightbulb icon found at the bottom of all context source cards to see your list of new story angles.
Brainstorming parameters that impact the new story angle suggestions are set by default in your composer settings but can also be adjusted during the context selection process at the top of the page by selecting the green plus icon.