Along with my video and the author's, there is also this SCREENCAST to help you understand, not only the constant that links masses and distances with the attractive force between them, but how that ludicrously small value was determined in the first place.
Source: Hewitt, P. G. (2015). Conceptual Physics (12th ed.). Boston, MA: Pearson.
Source: HEWITT, P. G. (2015). CONCEPTUAL PHYSICS (12TH ED.). BOSTON, MA: PEARSON.