add section on How to interpret an 'and' or an 'or'

[nicolevasilevsky]

note to self, my powerpoint drawing is here: https://docs.google.com/presentation/d/1wnTZheMDf5RN7C2GU_LpHofgwZlaMdlvw7U2LvXcSi4/edit#slide=id.p