Newspapers and magazines offer editorial opinions on subjects of current interest to their readers. The editors of the publication make a claim (a statement of truth, of value or of policy) about a newsworthy subject in order to try to convince their readers to agree with their claim. For instance, an editorial might urge readers to vote for a particular candidate or to support a particular charity.
Readers are then invited to express their own opinions in response to editorials by writing letters to the publication. A reader's letter might be selected for publication on the editorial page or in the editorial column. If so, that letter might well be edited for conciseness. Thus, clarity of expression is doubly important.
Each publication has different guidelines for such letters. Those guidelines as well as the address to which the letter should be sent can usually be found where the editorials are found.
Here's some helpful advice about writing a letter to the editor:
Choose from among these links for more information: How to Write an Editorial, How to Write an Editorial (from San Diego City Schools), How to Write an Award-Winning Editorial, About.com Letter to the Editor - Writing Help, and WriteSource 2000 How to Write an Editorial.