"C. P. B.," Woodhaven, L. I.— "Kindly show by illustrative sentences the proper use of 'who' and 'whom.’"

"Who" is a relative and interrogative pronoun used in the nominative, as "Who did this?"; and in the objective, as "From whom did you hear it?" "Who" is always used substantively and as referring to one or more persons. In number, it is uninflected, being singular or plural as required by its antecedent. In case, it has "who" for its possessive and "whom" for its objective. Thus "who," being both singular and plural, may refer to an antecedent of any number or gender.
For further elucidation of the use of this pronoun see Fernald's "Connectives of English Speech," published by Funk & Wagnalls Company.