Format your essay in the proper APA Style: 12-point font, double-spaced, 1-inch margins.
Cite your source by author and then date of publication the way it appears in the publication. For example, if the source letter was written by Dr. Smith in 1998, you would cite like this: "According to a letter by Dr. Smith, all children should be weaned off their bottles by eighteen months of age (Smith, 1998); he also goes on to say that modern mother's cuddle their children too much."
If the source does not have a date -- some electronic resources do not -- put n.d for "no date." In the above example, it would be cited: (Smith, n.d.)
Include the page number or paragraph number if you include a direct quote from the author of the source letter: "According to a letter by Dr. Smith, all children should be weaned off their bottles by eighteen months of age (Smith, 1998); he also goes on to say, ' Modern mothers cuddle their children too much.' (p. 734)."
Create a reference list and submit along with your assignment. Your instructors may have called this a "Works Cited Page" or "Bibliography" but the principle is the same -- a list of all the research sources you consulted. The list must be arraigned with the authors in alphabetical order. Include the date, publication the letter was included in, date and pages of the source.
An example would be: Smith, John Edward, PhD. (July, 1998). Overly Indulgent Parenting [Letter to the Editor]. Psychology Today. 101