If the omission is at the end of a quotation, add a fourth period to end the sentence. If you add something to a quotation, put it in square brackets. The most recent practice is to double space the indented material so it looks just like the rest of your paper. If you do not mention the author's name in the lead-in, put it in parentheses along with the page number. For more detailed explanations consult either the MLA or APA manual accordingly.
Page numbers are demonstrational.