Hila Qu discusses how to build a growth model, which is an equation that maps the key variables and user journey in a business to understand how they translate to growth. She outlines the following steps: 1. Identify a "North Star" metric that indicates the core value delivered to users. 2. Map the user journey from a new user to achieving the North Star. 3. Assemble the growth model by translating steps into variables and mapping how they relate in an equation. The growth model provides a framework to systematically grow a business by identifying leverage points and focusing efforts.